:root {
  --font-primary: 'Satoshi', system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  --font-serif: 'Source Serif 4', Georgia, "Times New Roman", serif;

  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --radius-xl: 22px;

  --container-max: 1240px;
  --container-narrow: 820px;
  --header-height: 72px;

  --transition-fast: 140ms ease;
  --transition-med: 220ms ease;
  --transition-slow: 360ms cubic-bezier(.2,.7,.2,1);
}

[data-theme="light"] {
  --canvas: #F6F0E6;
  --canvas-elevated: #FBF8F2;

  --surface: #F2E9DA;
  --surface-strong: #E8DDCB;
  --surface-acrylic: rgba(246, 240, 230, .92);

  --card-bg: #FCF9F3;
  --card-hover: #F5EEE3;

  --text-primary: #263425;
  --text-secondary: #625B4C;
  --text-muted: #8D8473;

  --accent: #B86619;
  --accent-strong: #934B0E;
  --accent-bg: rgba(184, 102, 25, .09);

  --violet: #6B5AA6;
  --violet-bg: rgba(107, 90, 166, .09);

  --mint: #557B68;
  --mint-bg: rgba(85, 123, 104, .10);

  --amber: #A47722;
  --amber-bg: rgba(164, 119, 34, .10);

  --danger: #A83D42;
  --danger-bg: rgba(168, 61, 66, .09);

  --keyline: #DDD2C1;
  --keyline-strong: #C9BCA8;

  --glow: rgba(184, 102, 25, .10);

  --input-bg: #FFFDF8;

  --btn-primary-bg: #B86619;
  --btn-primary-text: #FFF9F0;

  --correct-bg: rgba(85, 123, 104, .11);
  --correct-border: #557B68;

  --wrong-bg: rgba(168, 61, 66, .10);
  --wrong-border: #A83D42;

  --shadow-sm: 0 1px 2px rgba(58, 45, 28, .06);
  --shadow-md: 0 8px 24px rgba(58, 45, 28, .08);
  --shadow-lg: 0 18px 45px rgba(58, 45, 28, .12);

  color-scheme: light;
}

[data-theme="dark"] {
  --canvas: #07111C;
  --canvas-elevated: #0B1624;

  --surface: #101D2C;
  --surface-strong: #172638;
  --surface-acrylic: rgba(7, 17, 28, .92);

  --card-bg: #0D1A29;
  --card-hover: #132437;

  --text-primary: #F4F1EA;
  --text-secondary: #B9C2CE;
  --text-muted: #718094;

  --accent: #9C8BFF;
  --accent-strong: #B4A7FF;
  --accent-bg: rgba(156, 139, 255, .10);

  --violet: #9C8BFF;
  --violet-bg: rgba(156, 139, 255, .10);

  --mint: #36C5C8;
  --mint-bg: rgba(54, 197, 200, .10);

  --amber: #D8A64B;
  --amber-bg: rgba(216, 166, 75, .10);

  --danger: #F07A86;
  --danger-bg: rgba(240, 122, 134, .10);

  --keyline: rgba(170, 190, 215, .16);
  --keyline-strong: rgba(170, 190, 215, .28);

  --glow: rgba(156, 139, 255, .12);

  --input-bg: #091522;

  --btn-primary-bg: #9C8BFF;
  --btn-primary-text: #07111C;

  --correct-bg: rgba(54, 197, 200, .11);
  --correct-border: #36C5C8;

  --wrong-bg: rgba(240, 122, 134, .11);
  --wrong-border: #F07A86;

  --shadow-sm: 0 1px 3px rgba(0, 0, 0, .22);
  --shadow-md: 0 10px 30px rgba(0, 0, 0, .28);
  --shadow-lg: 0 20px 60px rgba(0, 0, 0, .36);

  color-scheme: dark;
}

*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-family: var(--font-primary);
  font-size: 16px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  scroll-behavior: smooth;
}

body {
  background: var(--canvas);
  color: var(--text-primary);
  min-height: 100vh;
}

a {
  color: var(--accent);
  text-decoration: none;
  transition: color var(--transition-fast);
}

a:hover {
  color: var(--accent-strong);
}

button,
input,
textarea,
select {
  font: inherit;
}

img {
  max-width: 100%;
  display: block;
}

strong {
  font-weight: 650;
}

::selection {
  background: var(--accent-bg);
  color: var(--accent-strong);
}

:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 3px;
  border-radius: 4px;
}

.app {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

.main {
  flex: 1;
  padding-top: var(--header-height);
}

.container {
  width: 100%;
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 32px;
}

.container-narrow {
  max-width: var(--container-narrow);
}

.section {
  padding: 72px 0;
}

.section-alt {
  background: var(--canvas-elevated);
}

.section-title {
  font-family: var(--font-serif);
  font-size: clamp(30px, 4vw, 40px);
  line-height: 1.15;
  font-weight: 600;
  margin-bottom: 10px;
  letter-spacing: -.025em;
}

.section-subtitle {
  color: var(--text-secondary);
  font-size: 17px;
  line-height: 1.7;
  margin-bottom: 36px;
  max-width: 680px;
}

.section-header-row {
  display: flex;
  align-items: flex-end;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 20px;
  margin-bottom: 32px;
}

.section-header-row .section-title {
  margin-bottom: 0;
}

.header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--header-height);
  background: var(--surface-acrylic);
  -webkit-backdrop-filter: blur(16px);
  backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--keyline);
  z-index: 100;
}

.header-inner {
  max-width: var(--container-max);
  margin: 0 auto;
  padding: 0 32px;
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
}

.brand {
  display: flex;
  align-items: center;
  gap: 9px;
  color: var(--text-primary);
  font-weight: 750;
  font-size: 19px;
  letter-spacing: -.015em;
}

.brand:hover {
  color: var(--text-primary);
}

.brand-logo {
  width: 164px;
  height: 46px;
  object-fit: contain;
  object-position: left center;
}

.brand-logo-dark {
  display: none;
}

[data-theme="dark"] .brand-logo-light {
  display: none;
}

[data-theme="dark"] .brand-logo-dark {
  display: block;
}

.brand-icon {
  font-size: 22px;
  color: var(--accent);
}

.brand-sep {
  color: var(--accent);
  font-weight: 500;
}

.black-hole-lab-section {
  position: relative;
}

.lab-kicker {
  display: block;
  margin-bottom: 7px;
  color: var(--accent);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: .12em;
}

.model-status {
  padding: 7px 11px;
  border: 1px solid var(--keyline);
  border-radius: 999px;
  color: var(--text-muted);
  font-size: 12px;
  font-weight: 600;
}

.model-status.ready {
  border-color: var(--mint);
  color: var(--mint);
}

.black-hole-lab {
  display: grid;
  grid-template-columns: minmax(0, 1.35fr) minmax(250px, .65fr);
  overflow: hidden;
  border: 1px solid var(--keyline);
  border-radius: var(--radius-xl);
  background: var(--card-bg);
  box-shadow: var(--shadow-md);
}

.model-stage {
  position: relative;
  min-height: 430px;
  overflow: hidden;
  touch-action: none;
  background: radial-gradient(circle at 50% 47%, var(--accent-bg), transparent 30%), radial-gradient(circle at 15% 15%, var(--violet-bg), transparent 35%), var(--surface);
}

.model-stage::before,
.model-stage::after {
  position: absolute;
  z-index: 1;
  pointer-events: none;
  color: var(--text-muted);
  font: 500 11px/1 var(--font-primary);
  letter-spacing: .08em;
}

.model-stage::before {
  content: 'BLACK HOLE / 3D STUDY';
  top: 20px;
  left: 22px;
}

.model-stage::after {
  content: 'DRAG TO ROTATE · SCROLL TO ZOOM';
  right: 22px;
  bottom: 20px;
}

.model-stage canvas {
  display: block;
  width: 100%;
  height: 100%;
}

.model-stage.model-unavailable {
  display: grid;
  place-items: center;
  color: var(--text-muted);
}

.model-stage.model-unavailable p {
  position: relative;
  z-index: 2;
  max-width: 250px;
  margin-top: 175px;
  text-align: center;
  font-size: 13px;
  line-height: 1.6;
}

.fallback-orbit {
  position: absolute;
  width: 235px;
  height: 74px;
  border: 2px solid var(--accent);
  border-radius: 50%;
  box-shadow: 0 0 35px var(--accent-bg);
  transform: rotate(-12deg);
  animation: modelFallbackOrbit 8s linear infinite;
}

.fallback-core {
  position: absolute;
  width: 106px;
  height: 106px;
  border: 12px solid var(--violet);
  border-radius: 50%;
  background: var(--canvas);
  box-shadow: 0 0 45px var(--violet-bg);
}

@keyframes modelFallbackOrbit {
  from { transform: rotate(-12deg) rotateY(0); }
  to { transform: rotate(-12deg) rotateY(360deg); }
}

.model-insights {
  display: flex;
  flex-direction: column;
  gap: 22px;
  padding: 34px 30px;
  border-left: 1px solid var(--keyline);
  background: var(--canvas-elevated);
}

.model-insight {
  display: grid;
  grid-template-columns: 32px 1fr;
  gap: 10px;
}

.model-insight > span {
  color: var(--accent);
  font: 600 12px/1 var(--font-primary);
}

.model-insight strong {
  font-size: 14px;
}

.model-insight p {
  margin-top: 3px;
  color: var(--text-secondary);
  font-size: 13px;
  line-height: 1.6;
}

.model-insights .btn {
  margin-top: auto;
  align-self: flex-start;
}

.spacetime-link {
  display: inline-flex;
  align-items: center;
  margin-top: -8px;
  color: var(--violet);
  font-size: 13px;
  font-weight: 650;
}

.spacetime-link:hover {
  color: var(--accent);
}

.model-switcher {
  display: grid;
  grid-template-columns: 1fr 1fr;
  padding: 4px;
  border: 1px solid var(--keyline);
  border-radius: 10px;
  background: var(--surface);
}

.model-choice {
  padding: 8px 6px;
  border: 0;
  border-radius: 7px;
  background: transparent;
  color: var(--text-muted);
  font: 600 12px/1 var(--font-primary);
  cursor: pointer;
}

.model-choice.active {
  background: var(--card-bg);
  color: var(--accent);
  box-shadow: var(--shadow-sm);
}

@media (max-width: 760px) {
  .brand-logo { width: 136px; }
  .black-hole-lab { grid-template-columns: 1fr; }
  .model-stage { min-height: 340px; }
  .model-insights { border-top: 1px solid var(--keyline); border-left: 0; }
  .model-stage::after { right: auto; left: 22px; }
}

.nav {
  display: flex;
  align-items: center;
  gap: 28px;
}

.nav-link {
  position: relative;
  padding: 8px 0;
  border-radius: 0;
  color: var(--text-secondary);
  font-weight: 500;
  font-size: 14px;
  transition: color var(--transition-fast);
}

.nav-link::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 1px;
  height: 2px;
  background: var(--accent);
  transform: scaleX(0);
  transform-origin: center;
  transition: transform var(--transition-fast);
}

.nav-link:hover {
  color: var(--text-primary);
  background: transparent;
}

.nav-link.active {
  color: var(--accent);
  background: transparent;
}

.nav-link.active::after {
  transform: scaleX(1);
}

.header-actions {
  display: flex;
  align-items: center;
  gap: 8px;
}

.learning-access {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  min-height: 36px;
  padding: 0 12px;
  border: 1px solid var(--keyline);
  border-radius: 999px;
  color: var(--text-secondary);
  font-size: 12px;
  font-weight: 650;
  white-space: nowrap;
  transition: border-color var(--transition-fast), background var(--transition-fast), color var(--transition-fast), transform var(--transition-fast);
}

.learning-access:hover {
  border-color: var(--accent);
  background: var(--accent-bg);
  color: var(--accent);
  transform: translateY(-1px);
}

.learning-access-dot {
  width: 7px;
  height: 7px;
  border-radius: 50%;
  background: var(--mint);
  box-shadow: 0 0 0 4px var(--mint-bg);
}

.btn-icon {
  width: 42px;
  height: 42px;
  border-radius: 10px;
  border: 1px solid var(--keyline);
  background: transparent;
  color: var(--text-secondary);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all var(--transition-fast);
}

.btn-icon:hover {
  color: var(--text-primary);
  border-color: var(--keyline-strong);
  background: var(--surface);
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 10px 20px;
  min-height: 42px;
  border-radius: 9px;
  font-family: var(--font-primary);
  font-weight: 600;
  font-size: 14px;
  border: 1px solid transparent;
  cursor: pointer;
  transition:
    background var(--transition-fast),
    border-color var(--transition-fast),
    color var(--transition-fast),
    transform var(--transition-fast),
    box-shadow var(--transition-fast);
  white-space: nowrap;
}

.btn-primary {
  background: var(--btn-primary-bg);
  color: var(--btn-primary-text);
  border-color: var(--btn-primary-bg);
}

.btn-primary:hover {
  background: var(--accent-strong);
  color: var(--btn-primary-text);
  transform: translateY(-1px);
  box-shadow: var(--shadow-sm);
}

.btn-outline {
  background: transparent;
  color: var(--text-primary);
  border-color: var(--keyline-strong);
}

.btn-outline:hover {
  border-color: var(--accent);
  color: var(--accent);
  background: var(--accent-bg);
}

.btn-lg {
  padding: 13px 26px;
  min-height: 48px;
  font-size: 15px;
  border-radius: 10px;
}

.hero {
  position: relative;
  min-height: 480px;
  display: flex;
  align-items: center;
  justify-content: center;
  overflow: hidden;
  background: var(--canvas);
  border-bottom: 1px solid var(--keyline);
}

.hero-ambient {
  position: absolute;
  inset: 0;
  background:
    radial-gradient(circle at 20% 50%, var(--accent-bg), transparent 34%),
    radial-gradient(circle at 80% 30%, var(--violet-bg), transparent 30%);
  pointer-events: none;
  opacity: .7;
}

.hero-content {
  text-align: center;
  max-width: 780px;
  padding: 88px 24px;
  position: relative;
  z-index: 1;
}

.hero-label {
  display: inline-block;
  font-size: 11px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: .16em;
  color: var(--accent);
  margin-bottom: 18px;
}

.hero-title {
  font-family: var(--font-serif);
  font-size: clamp(38px, 6vw, 68px);
  font-weight: 600;
  line-height: 1.05;
  letter-spacing: -.035em;
  margin-bottom: 22px;
}

.hero-subtitle {
  display: flex;
  gap: 10px;
  justify-content: center;
  flex-wrap: wrap;
  margin-bottom: 32px;
}

.meta-badge {
  display: inline-flex;
  align-items: center;
  gap: 5px;
  padding: 5px 11px;
  border-radius: 999px;
  font-size: 12px;
  font-weight: 500;
  background: transparent;
  color: var(--text-secondary);
  border: 1px solid var(--keyline);
}

.topic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(340px, 1fr));
  gap: 24px;
}

.topic-card {
  position: relative;
  background: var(--card-bg);
  border: 1px solid var(--keyline);
  border-radius: var(--radius-lg);
  overflow: hidden;
  transition:
    transform var(--transition-med),
    border-color var(--transition-med),
    box-shadow var(--transition-med),
    background var(--transition-med);
  display: block;
  color: var(--text-primary);
}

.topic-card:hover {
  border-color: var(--keyline-strong);
  background: var(--card-hover);
  transform: translateY(-3px);
  box-shadow: var(--shadow-md);
  color: var(--text-primary);
}

.topic-card-hero {
  height: 174px;
  display: flex;
  align-items: center;
  justify-content: center;
  background:
    linear-gradient(135deg, var(--surface), var(--canvas-elevated));
  border-bottom: 1px solid var(--keyline);
  font-size: 58px;
}

.topic-card-hero img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.topic-card-body {
  padding: 25px 26px 23px;
}

.topic-card-domain {
  display: inline-block;
  font-size: 11px;
  font-weight: 750;
  text-transform: uppercase;
  letter-spacing: .13em;
  color: var(--accent);
  margin-bottom: 9px;
}

.topic-card-title {
  font-family: var(--font-serif);
  font-size: 27px;
  line-height: 1.15;
  font-weight: 600;
  margin: 0 0 8px;
  letter-spacing: -.02em;
}

.topic-card-subtitle {
  color: var(--text-secondary);
  font-size: 15px;
  line-height: 1.55;
  margin-bottom: 19px;
}

.topic-card-meta {
  display: flex;
  gap: 17px;
  flex-wrap: wrap;
  padding-top: 16px;
  border-top: 1px solid var(--keyline);
  font-size: 12px;
  color: var(--text-muted);
}

.feature-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  border-top: 1px solid var(--keyline);
  border-left: 1px solid var(--keyline);
}

.feature-card {
  background: transparent;
  border-right: 1px solid var(--keyline);
  border-bottom: 1px solid var(--keyline);
  border-radius: 0;
  padding: 30px 26px;
  transition: background var(--transition-med);
}

.feature-card:hover {
  background: var(--card-hover);
}

.feature-icon {
  font-size: 27px;
  margin-bottom: 16px;
}

.feature-card h3 {
  font-family: var(--font-serif);
  font-size: 20px;
  font-weight: 600;
  margin-bottom: 8px;
}

.feature-card p {
  color: var(--text-secondary);
  font-size: 14px;
  line-height: 1.65;
}

.topic-hero {
  position: relative;
  background: var(--canvas);
  padding: 76px 0 48px;
  border-bottom: 1px solid var(--keyline);
}

.topic-hero-bg {
  position: absolute;
  inset: 0;
  background:
    radial-gradient(circle at 80% 40%, var(--accent-bg), transparent 34%);
  pointer-events: none;
}

.topic-hero-content {
  display: flex;
  align-items: center;
  gap: 28px;
  position: relative;
  z-index: 1;
}

.topic-hero-emoji {
  width: 112px;
  height: 112px;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  border: 1px solid var(--keyline);
  border-radius: var(--radius-lg);
  background: var(--surface);
  font-size: 62px;
}

.topic-hero-title {
  font-family: var(--font-serif);
  font-size: clamp(36px, 5vw, 54px);
  font-weight: 600;
  line-height: 1.08;
  letter-spacing: -.03em;
  margin: 7px 0;
}

.topic-hero-subtitle {
  color: var(--text-secondary);
  font-size: 18px;
  line-height: 1.6;
  margin-bottom: 13px;
}

.topic-hero-meta {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}

.back-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 13px;
  font-weight: 550;
  color: var(--text-secondary);
  margin-bottom: 18px;
}

.back-link:hover {
  color: var(--accent);
}

.essential-question {
  font-family: var(--font-serif);
  font-size: clamp(22px, 3vw, 31px);
  font-style: italic;
  line-height: 1.45;
  padding: 28px 30px;
  border-left: 3px solid var(--accent);
  background: var(--accent-bg);
  border-radius: 0 var(--radius-md) var(--radius-md) 0;
  margin-bottom: 24px;
}

.eq-label {
  display: block;
  font-family: var(--font-primary);
  font-size: 10px;
  font-weight: 750;
  text-transform: uppercase;
  letter-spacing: .14em;
  color: var(--accent);
  font-style: normal;
  margin-bottom: 9px;
}

.topic-summary {
  font-size: 17px;
  color: var(--text-secondary);
  max-width: 720px;
  line-height: 1.75;
}

.quick-actions {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  border-top: 1px solid var(--keyline);
  border-left: 1px solid var(--keyline);
}

.action-card {
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  gap: 7px;
  padding: 25px 22px;
  background: transparent;
  border-right: 1px solid var(--keyline);
  border-bottom: 1px solid var(--keyline);
  border-radius: 0;
  text-align: left;
  transition: background var(--transition-med), color var(--transition-med);
  color: var(--text-primary);
}

.action-card:hover {
  transform: none;
  box-shadow: none;
  color: var(--text-primary);
  background: var(--card-hover);
}

.action-quiz:hover {
  border-color: var(--keyline);
  background: var(--mint-bg);
}

.action-flash:hover {
  border-color: var(--keyline);
  background: var(--violet-bg);
}

.action-tutor:hover {
  border-color: var(--keyline);
  background: var(--accent-bg);
}

.action-timeline:hover {
  border-color: var(--keyline);
  background: var(--amber-bg);
}

.action-icon {
  font-size: 26px;
  margin-bottom: 4px;
}

.action-label {
  font-family: var(--font-serif);
  font-weight: 600;
  font-size: 18px;
}

.action-desc {
  font-size: 13px;
  color: var(--text-muted);
  line-height: 1.5;
}

.concept-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 16px;
}

.concept-card {
  display: block;
  padding: 24px;
  background: var(--card-bg);
  border: 1px solid var(--keyline);
  border-radius: var(--radius-md);
  transition:
    border-color var(--transition-med),
    background var(--transition-med),
    transform var(--transition-med);
  color: var(--text-primary);
  animation: fadeInUp .4s ease both;
  animation-delay: var(--delay);
}

.concept-card:hover {
  border-color: var(--keyline-strong);
  background: var(--card-hover);
  transform: translateY(-2px);
  color: var(--text-primary);
}

@keyframes fadeInUp {
  from {
    opacity: 0;
    transform: translateY(10px);
  }

  to {
    opacity: 1;
    transform: translateY(0);
  }
}

.concept-difficulty {
  font-size: 10px;
  letter-spacing: .14em;
  text-transform: uppercase;
  color: var(--amber);
  margin-bottom: 9px;
}

.concept-card-title {
  font-family: var(--font-serif);
  font-size: 19px;
  font-weight: 600;
  margin-bottom: 8px;
}

.concept-card-def {
  font-size: 14px;
  color: var(--text-secondary);
  line-height: 1.6;
  display: -webkit-box;
  -webkit-line-clamp: 3;
  line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

.timeline-preview {
  position: relative;
  padding-left: 32px;
}

.timeline-item {
  position: relative;
  padding-bottom: 32px;
  display: grid;
  grid-template-columns: 100px 1fr;
  gap: 24px;
}

.timeline-date {
  font-size: 13px;
  font-weight: 650;
  color: var(--accent);
  text-align: right;
  padding-top: 2px;
}

.timeline-dot {
  position: absolute;
  left: 100px;
  top: 6px;
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: var(--accent);
  border: 3px solid var(--canvas);
  transform: translateX(6px);
  z-index: 1;
}

.timeline-content {
  padding-left: 24px;
  border-left: 1px solid var(--keyline-strong);
  padding-bottom: 12px;
}

.timeline-content strong {
  display: block;
  margin-bottom: 4px;
  font-family: var(--font-serif);
  font-size: 18px;
}

.timeline-content p {
  font-size: 14px;
  color: var(--text-secondary);
  line-height: 1.6;
}

.timeline-full {
  position: relative;
  padding-left: 2px;
}

.timeline-item-full {
  display: grid;
  grid-template-columns: 24px 1fr;
  gap: 20px;
  padding-bottom: 8px;
  animation: fadeInUp .4s ease both;
  animation-delay: var(--delay);
}

.timeline-line-segment {
  position: absolute;
  left: 11px;
  top: 0;
  bottom: 0;
  width: 1px;
  background: var(--keyline);
}

.timeline-marker {
  width: 24px;
  height: 24px;
  border-radius: 50%;
  background: var(--accent);
  border: 5px solid var(--canvas);
  position: relative;
  z-index: 1;
  flex-shrink: 0;
}

.timeline-event-card {
  background: var(--card-bg);
  border: 1px solid var(--keyline);
  border-radius: var(--radius-md);
  padding: 23px;
  margin-bottom: 24px;
}

.timeline-event-date {
  font-size: 12px;
  font-weight: 650;
  color: var(--accent);
}

.timeline-event-title {
  font-family: var(--font-serif);
  font-size: 20px;
  font-weight: 600;
  margin: 6px 0 8px;
}

.timeline-event-desc {
  font-size: 15px;
  color: var(--text-secondary);
  line-height: 1.65;
  margin-bottom: 12px;
}

.timeline-event-source {
  font-size: 12px;
  color: var(--text-muted);
}

.sources-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}

.source-item {
  display: flex;
  gap: 16px;
  align-items: flex-start;
  padding: 16px;
  background: var(--card-bg);
  border: 1px solid var(--keyline);
  border-radius: var(--radius-sm);
}

.source-item-sm {
  padding: 12px;
}

.source-type {
  padding: 3px 9px;
  border-radius: 999px;
  font-size: 10px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: .06em;
  white-space: nowrap;
  background: var(--violet-bg);
  color: var(--violet);
  border: 1px solid var(--violet);
}

.source-meta {
  font-size: 13px;
  color: var(--text-muted);
  margin-top: 2px;
}

.concept-header {
  margin-bottom: 34px;
}

.concept-difficulty-lg {
  font-size: 11px;
  text-transform: uppercase;
  letter-spacing: .15em;
  color: var(--amber);
  margin-bottom: 9px;
}

.concept-definition {
  font-size: 20px;
  font-family: var(--font-serif);
  color: var(--text-secondary);
  line-height: 1.65;
  margin-top: 13px;
  max-width: 760px;
}

.page-title {
  font-family: var(--font-serif);
  font-size: clamp(30px, 4vw, 46px);
  font-weight: 600;
  line-height: 1.1;
  letter-spacing: -.025em;
  margin-bottom: 9px;
}

.level-selector {
  display: flex;
  gap: 3px;
  flex-wrap: wrap;
  margin-bottom: 24px;
  padding: 4px;
  background: var(--surface);
  border-radius: 10px;
  border: 1px solid var(--keyline);
}

.level-btn {
  padding: 9px 15px;
  border: none;
  border-radius: 7px;
  background: transparent;
  color: var(--text-secondary);
  font-family: var(--font-primary);
  font-weight: 550;
  font-size: 13px;
  cursor: pointer;
  transition: all var(--transition-fast);
  flex: 1;
  min-width: 0;
}

.level-btn:hover {
  color: var(--text-primary);
  background: var(--keyline);
}

.level-btn.active {
  background: var(--card-bg);
  color: var(--accent);
  box-shadow: var(--shadow-sm);
}

.explanation-panel {
  display: none;
  padding: 30px;
  background: var(--card-bg);
  border: 1px solid var(--keyline);
  border-radius: var(--radius-md);
  margin-bottom: 32px;
  line-height: 1.8;
  font-size: 16px;
}

.explanation-panel.active {
  display: block;
}

.explanation-content p {
  margin-bottom: 12px;
}

.explanation-content p:last-child {
  margin-bottom: 0;
}

.concept-section {
  margin-top: 42px;
  padding-top: 32px;
  border-top: 1px solid var(--keyline);
}

.concept-section-title {
  font-family: var(--font-serif);
  font-size: 25px;
  font-weight: 600;
  margin-bottom: 20px;
}

.analogy-card {
  padding: 20px 24px;
  background: var(--accent-bg);
  border-left: 3px solid var(--accent);
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  margin-bottom: 12px;
  font-size: 15px;
  line-height: 1.7;
}

.misconception-card {
  border: 1px solid var(--keyline);
  border-radius: var(--radius-md);
  overflow: hidden;
  margin-bottom: 16px;
}

.misconception-claim {
  display: flex;
  gap: 16px;
  align-items: flex-start;
  padding: 20px;
  background: var(--wrong-bg);
  border-bottom: 1px solid var(--keyline);
}

.misconception-correction {
  display: flex;
  gap: 16px;
  align-items: flex-start;
  padding: 20px;
  background: var(--correct-bg);
}

.misconception-icon {
  width: 28px;
  height: 28px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-shrink: 0;
  font-weight: 700;
  font-size: 13px;
  background: var(--wrong-border);
  color: #fff;
}

.misconception-icon.correct {
  background: var(--correct-border);
}

.misconception-claim p,
.misconception-correction p {
  font-size: 15px;
  line-height: 1.6;
}

.quiz-progress-bar {
  height: 5px;
  background: var(--surface);
  border-radius: 999px;
  margin-bottom: 16px;
  overflow: hidden;
}

.quiz-progress-fill {
  height: 100%;
  background: var(--accent);
  border-radius: 999px;
  transition: width .5s ease;
}

.quiz-counter {
  text-align: center;
  font-size: 13px;
  color: var(--text-muted);
  margin-bottom: 32px;
}

.quiz-question-full {
  display: none;
}

.quiz-question-full.active {
  display: block;
}

.quiz-q-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 16px;
}

.quiz-q-num {
  font-weight: 700;
  color: var(--accent);
  font-size: 14px;
}

.quiz-q-diff {
  font-size: 10px;
  text-transform: uppercase;
  letter-spacing: .13em;
  color: var(--amber);
}

.quiz-prompt-lg {
  font-family: var(--font-serif);
  font-size: 25px;
  font-weight: 600;
  margin-bottom: 28px;
  line-height: 1.4;
}

.quiz-options-lg {
  display: flex;
  flex-direction: column;
  gap: 10px;
  margin-bottom: 24px;
}

.quiz-option-lg {
  display: flex;
  align-items: center;
  gap: 15px;
  padding: 16px 20px;
  background: var(--card-bg);
  border: 1px solid var(--keyline);
  border-radius: var(--radius-md);
  font-size: 15px;
  font-family: var(--font-primary);
  color: var(--text-primary);
  cursor: pointer;
  transition: all var(--transition-fast);
  text-align: left;
  width: 100%;
}

.quiz-option-lg:hover:not(.answered) {
  border-color: var(--accent);
  background: var(--accent-bg);
}

.opt-letter {
  width: 30px;
  height: 30px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: 700;
  font-size: 12px;
  background: var(--surface);
  flex-shrink: 0;
  border: 1px solid var(--keyline);
}

.quiz-option-lg.correct {
  border-color: var(--correct-border);
  background: var(--correct-bg);
}

.quiz-option-lg.correct .opt-letter {
  background: var(--correct-border);
  color: #fff;
}

.quiz-option-lg.wrong {
  border-color: var(--wrong-border);
  background: var(--wrong-bg);
}

.quiz-option-lg.wrong .opt-letter {
  background: var(--wrong-border);
  color: #fff;
}

.quiz-option-lg.answered {
  pointer-events: none;
  opacity: .7;
}

.quiz-option-lg.answered.correct,
.quiz-option-lg.answered.wrong {
  opacity: 1;
}

.quiz-explanation {
  padding: 20px 24px;
  background: var(--surface);
  border-radius: var(--radius-md);
  font-size: 15px;
  line-height: 1.7;
  margin-bottom: 16px;
  border: 1px solid var(--keyline);
}

.quiz-next {
  width: 100%;
  justify-content: center;
  padding: 13px;
  font-size: 14px;
}

.hidden {
  display: none !important;
}

.quiz-question {
  display: none;
}

.quiz-question.active {
  display: block;
}

.quiz-prompt {
  font-size: 17px;
  font-weight: 600;
  margin-bottom: 16px;
}

.quiz-options {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.quiz-option {
  padding: 14px 18px;
  background: var(--card-bg);
  border: 1px solid var(--keyline);
  border-radius: var(--radius-sm);
  font-size: 15px;
  font-family: var(--font-primary);
  color: var(--text-primary);
  cursor: pointer;
  transition: all var(--transition-fast);
  text-align: left;
  width: 100%;
}

.quiz-option:hover {
  border-color: var(--accent);
  background: var(--accent-bg);
}

.quiz-feedback {
  padding: 16px;
  border-radius: var(--radius-sm);
  margin-top: 12px;
  font-size: 14px;
  line-height: 1.6;
}

.results-card {
  text-align: center;
  padding: 52px 32px;
  background: var(--card-bg);
  border: 1px solid var(--keyline);
  border-radius: var(--radius-lg);
}

.results-title {
  font-family: var(--font-serif);
  font-size: 34px;
  font-weight: 600;
  margin-bottom: 24px;
}

.results-score {
  display: flex;
  justify-content: center;
  align-items: baseline;
  gap: 8px;
  margin-bottom: 16px;
}

.score-num {
  font-size: 68px;
  font-weight: 700;
  color: var(--mint);
}

.score-sep {
  font-size: 42px;
  color: var(--text-muted);
}

.score-total {
  font-size: 46px;
  font-weight: 600;
  color: var(--text-secondary);
}

.results-message {
  font-size: 17px;
  color: var(--text-secondary);
  margin-bottom: 32px;
}

.results-actions {
  display: flex;
  gap: 12px;
  justify-content: center;
  flex-wrap: wrap;
}

.flashcard-deck {
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.flashcard {
  cursor: pointer;
  perspective: 1000px;
}

.flashcard-inner {
  position: relative;
  min-height: 120px;
  transition: transform .5s ease;
  transform-style: preserve-3d;
}

.flashcard[data-flipped="true"] .flashcard-inner {
  transform: rotateX(180deg);
}

.flashcard-front,
.flashcard-back {
  position: absolute;
  inset: 0;
  padding: 24px;
  border-radius: var(--radius-md);
  backface-visibility: hidden;
  display: flex;
  flex-direction: column;
  justify-content: center;
}

.flashcard-front {
  background: var(--card-bg);
  border: 1px solid var(--keyline);
}

.flashcard-back {
  background: var(--accent-bg);
  border: 1px solid var(--accent);
  transform: rotateX(180deg);
}

.flashcard-hint {
  font-size: 12px;
  color: var(--text-muted);
  margin-top: 8px;
}

.flashcard-viewer {
  text-align: center;
}

.flashcard-counter {
  font-size: 14px;
  color: var(--text-muted);
  margin-bottom: 24px;
}

.flashcard-stage {
  position: relative;
  min-height: 280px;
  margin-bottom: 24px;
}

.flashcard-large {
  display: none;
  perspective: 1000px;
}

.flashcard-large.active {
  display: block;
}

.flashcard-large-inner {
  position: relative;
  min-height: 280px;
  transition: transform .5s ease;
  transform-style: preserve-3d;
  cursor: pointer;
}

.flashcard-large[data-flipped="true"] .flashcard-large-inner {
  transform: rotateX(180deg);
}

.flashcard-large-front,
.flashcard-large-back {
  position: absolute;
  inset: 0;
  padding: 40px 32px;
  border-radius: var(--radius-lg);
  backface-visibility: hidden;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
}

.flashcard-large-front {
  background: var(--card-bg);
  border: 1px solid var(--keyline);
  font-size: 21px;
  font-weight: 500;
  line-height: 1.5;
}

.flashcard-large-back {
  background: var(--accent-bg);
  border: 1px solid var(--accent);
  transform: rotateX(180deg);
  font-size: 16px;
  line-height: 1.7;
}

.flashcard-controls {
  display: flex;
  gap: 10px;
  justify-content: center;
  margin-bottom: 24px;
}

.flashcard-rate {
  padding: 20px;
  background: var(--surface);
  border-radius: var(--radius-md);
  border: 1px solid var(--keyline);
}

.flashcard-rate p {
  font-size: 14px;
  color: var(--text-muted);
  margin-bottom: 12px;
}

.rate-buttons {
  display: flex;
  gap: 10px;
  justify-content: center;
}

.rate-btn {
  padding: 10px 18px;
  border: 1px solid var(--keyline);
  border-radius: var(--radius-sm);
  background: var(--card-bg);
  color: var(--text-primary);
  font-family: var(--font-primary);
  font-size: 14px;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.rate-btn:hover {
  transform: translateY(-1px);
}

.rate-hard:hover {
  border-color: var(--danger);
  background: var(--wrong-bg);
}

.rate-ok:hover {
  border-color: var(--amber);
  background: var(--amber-bg);
}

.rate-easy:hover {
  border-color: var(--mint);
  background: var(--correct-bg);
}

.fc-stats {
  display: flex;
  gap: 32px;
  justify-content: center;
  margin: 24px 0;
}

.fc-stat {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
}

.fc-stat-num {
  font-size: 36px;
  font-weight: 700;
}

#fc-hard {
  color: var(--danger);
}

#fc-ok {
  color: var(--amber);
}

#fc-easy {
  color: var(--mint);
}

.tutor-chat {
  max-width: 100%;
}

.tutor-messages {
  display: flex;
  flex-direction: column;
  gap: 16px;
  margin-bottom: 24px;
  min-height: 200px;
  max-height: 500px;
  overflow-y: auto;
  padding: 18px;
  background: var(--surface);
  border-radius: var(--radius-lg);
  border: 1px solid var(--keyline);
}

.tutor-message {
  display: flex;
  gap: 12px;
  align-items: flex-start;
}

.tutor-msg-user {
  flex-direction: row-reverse;
}

.tutor-avatar {
  width: 36px;
  height: 36px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
  background: var(--card-bg);
  border: 1px solid var(--keyline);
  flex-shrink: 0;
}

.tutor-msg-user .tutor-avatar {
  background: var(--accent-bg);
  border-color: var(--accent);
}

.tutor-bubble {
  max-width: 80%;
  padding: 14px 18px;
  border-radius: var(--radius-md);
  font-size: 15px;
  line-height: 1.7;
  background: var(--card-bg);
  border: 1px solid var(--keyline);
}

.tutor-msg-user .tutor-bubble {
  background: var(--accent-bg);
  border-color: var(--accent);
}

.tutor-bubble p {
  margin-bottom: 8px;
}

.tutor-bubble p:last-child {
  margin-bottom: 0;
}

.tutor-sources {
  margin-top: 12px;
  padding-top: 12px;
  border-top: 1px solid var(--keyline);
  font-size: 13px;
  color: var(--text-muted);
}

.tutor-followup {
  margin-top: 8px;
  font-size: 14px;
  font-style: italic;
  color: var(--violet);
}

.tutor-copy {
  display: block;
  margin: 12px 0 0 auto;
  padding: 4px 0;
  border: 0;
  background: transparent;
  color: var(--text-muted);
  font-size: 12px;
  font-weight: 600;
  cursor: pointer;
}

.tutor-copy:hover {
  color: var(--accent);
}

.tutor-suggestions {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-bottom: 16px;
}

.suggestion-chip {
  padding: 8px 14px;
  border: 1px solid var(--keyline);
  border-radius: 999px;
  background: var(--card-bg);
  color: var(--text-secondary);
  font-family: var(--font-primary);
  font-size: 13px;
  cursor: pointer;
  transition: all var(--transition-fast);
}

.suggestion-chip:hover {
  border-color: var(--accent);
  color: var(--accent);
  background: var(--accent-bg);
}

.tutor-input-form {
  display: flex;
  gap: 10px;
}

.tutor-input {
  flex: 1;
  padding: 13px 17px;
  min-height: 46px;
  border: 1px solid var(--keyline);
  border-radius: var(--radius-md);
  background: var(--input-bg);
  color: var(--text-primary);
  font-family: var(--font-primary);
  font-size: 15px;
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.tutor-input::placeholder,
.search-input::placeholder {
  color: var(--text-muted);
}

.tutor-input:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-bg);
}

.search-form {
  display: flex;
  gap: 10px;
  margin-bottom: 32px;
}

.search-input {
  flex: 1;
  padding: 13px 17px;
  min-height: 48px;
  border: 1px solid var(--keyline);
  border-radius: var(--radius-md);
  background: var(--input-bg);
  color: var(--text-primary);
  font-family: var(--font-primary);
  font-size: 16px;
  transition: border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.search-input:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-bg);
}

.results-count {
  font-size: 13px;
  color: var(--text-muted);
  margin-bottom: 24px;
}

.results-section {
  margin-bottom: 32px;
}

.results-section h3 {
  font-family: var(--font-serif);
  font-size: 21px;
  font-weight: 600;
  margin-bottom: 16px;
  color: var(--text-primary);
}

.search-result-item {
  display: block;
  padding: 17px 20px;
  background: var(--card-bg);
  border: 1px solid var(--keyline);
  border-radius: var(--radius-sm);
  margin-bottom: 10px;
  transition: all var(--transition-fast);
  color: var(--text-primary);
}

.search-result-item:hover {
  border-color: var(--keyline-strong);
  background: var(--card-hover);
  color: var(--text-primary);
}

.result-topic {
  font-size: 11px;
  font-weight: 650;
  text-transform: uppercase;
  letter-spacing: .06em;
  color: var(--accent);
  margin-left: 10px;
}

.search-result-item p {
  font-size: 14px;
  color: var(--text-secondary);
  margin-top: 4px;
}

.search-suggestions {
  margin-top: 24px;
}

.search-suggestions h3 {
  font-family: var(--font-primary);
  font-size: 14px;
  color: var(--text-secondary);
  margin-bottom: 14px;
}

.suggestion-chips {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.chip {
  padding: 8px 14px;
  border: 1px solid var(--keyline);
  border-radius: 999px;
  font-size: 13px;
  color: var(--text-secondary);
  transition: all var(--transition-fast);
}

.chip:hover {
  border-color: var(--accent);
  color: var(--accent);
  background: var(--accent-bg);
}

.library-tabs {
  display: flex;
  gap: 24px;
  margin-bottom: 32px;
  border-bottom: 1px solid var(--keyline);
  padding-bottom: 0;
}

.lib-tab {
  position: relative;
  padding: 10px 0 13px;
  border: none;
  background: transparent;
  color: var(--text-secondary);
  font-family: var(--font-primary);
  font-weight: 550;
  font-size: 14px;
  cursor: pointer;
  border-bottom: 2px solid transparent;
  transition: color var(--transition-fast);
  margin-bottom: -1px;
}

.lib-tab:hover {
  color: var(--text-primary);
}

.lib-tab.active {
  color: var(--accent);
  border-bottom-color: var(--accent);
}

.lib-panel {
  display: none;
}

.lib-panel.active {
  display: block;
}

.empty-state {
  text-align: center;
  padding: 70px 24px;
  color: var(--text-secondary);
  border: 1px dashed var(--keyline-strong);
  border-radius: var(--radius-md);
}

.empty-state p {
  margin-bottom: 20px;
}

.save-control {
  margin-top: 18px;
  padding: 8px 12px;
  border: 1px solid var(--keyline-strong);
  border-radius: 999px;
  background: var(--card-bg);
  color: var(--text-secondary);
  font: 600 13px/1 var(--font-primary);
  cursor: pointer;
  transition: transform var(--transition-fast), border-color var(--transition-fast), background var(--transition-fast), color var(--transition-fast);
}

.save-control:hover,
.save-control.saved {
  border-color: var(--accent);
  background: var(--accent-bg);
  color: var(--accent);
}

.save-control:hover {
  transform: translateY(-1px);
}

.study-note {
  display: grid;
  gap: 14px;
  margin: 32px 0;
  padding: 24px;
  border: 1px solid var(--keyline);
  border-radius: var(--radius-lg);
  background: var(--surface);
}

.study-note-kicker {
  color: var(--accent);
  font-size: 11px;
  font-weight: 700;
  letter-spacing: .1em;
}

.study-note .concept-section-title {
  margin-top: 3px;
}

.study-note-input {
  width: 100%;
  resize: vertical;
  padding: 13px 15px;
  border: 1px solid var(--keyline);
  border-radius: var(--radius-md);
  background: var(--input-bg);
  color: var(--text-primary);
  font: inherit;
  line-height: 1.6;
}

.study-note-input:focus {
  outline: none;
  border-color: var(--accent);
  box-shadow: 0 0 0 3px var(--accent-bg);
}

.study-note-actions {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.study-note-status {
  color: var(--mint);
  font-size: 13px;
  font-weight: 600;
}

.saved-list {
  display: grid;
  gap: 12px;
}

.saved-item {
  display: grid;
  grid-template-columns: auto 1fr auto;
  gap: 12px;
  align-items: center;
  padding: 17px 18px;
  border: 1px solid var(--keyline);
  border-radius: var(--radius-md);
  background: var(--card-bg);
  color: var(--text-primary);
  transition: transform var(--transition-fast), border-color var(--transition-fast), box-shadow var(--transition-fast);
}

.saved-item:hover {
  border-color: var(--accent);
  box-shadow: var(--shadow-sm);
  transform: translateY(-1px);
}

.saved-item > span {
  color: var(--accent);
}

.saved-item small {
  color: var(--text-muted);
  font-size: 12px;
}

.saved-note {
  display: block;
}

.saved-note p {
  margin: 8px 0;
  color: var(--text-secondary);
  white-space: pre-wrap;
}

.progress-overview {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(160px, 1fr));
  gap: 16px;
}

.progress-stat {
  padding: 24px;
  background: var(--card-bg);
  border: 1px solid var(--keyline);
  border-radius: var(--radius-md);
  text-align: center;
}

.stat-num {
  display: block;
  font-size: 34px;
  font-weight: 700;
  color: var(--accent);
}

.stat-label {
  font-size: 13px;
  color: var(--text-muted);
  margin-top: 4px;
}

.footer {
  padding: 34px 0;
  border-top: 1px solid var(--keyline);
  text-align: center;
}

.footer-text {
  font-size: 12px;
  color: var(--text-muted);
}

.hidden {
  display: none !important;
}

@media (max-width: 960px) {
  .header-inner {
    padding: 0 24px;
  }

  .container {
    padding: 0 24px;
  }

  .nav {
    gap: 18px;
  }

  .quick-actions {
    grid-template-columns: repeat(2, 1fr);
  }

  .feature-grid {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (max-width: 768px) {
  .header-inner {
    padding: 0 16px;
  }

  .container {
    padding: 0 16px;
  }

  .main {
    padding-top: var(--header-height);
  }

  .nav {
    display: none;
  }

  .section {
    padding: 48px 0;
  }

  .section-header-row {
    align-items: flex-start;
  }

  .hero {
    min-height: 400px;
  }

  .hero-content {
    padding: 60px 16px;
  }

  .hero-title {
    font-size: clamp(38px, 11vw, 54px);
  }

  .topic-grid {
    grid-template-columns: 1fr;
  }

  .feature-grid {
    grid-template-columns: 1fr;
  }

  .quick-actions {
    grid-template-columns: 1fr 1fr;
  }

  .concept-grid {
    grid-template-columns: 1fr;
  }

  .topic-hero {
    padding: 58px 0 38px;
  }

  .topic-hero-content {
    flex-direction: column;
    align-items: flex-start;
    gap: 20px;
  }

  .topic-hero-emoji {
    width: 86px;
    height: 86px;
    font-size: 48px;
  }

  .topic-hero-title {
    font-size: clamp(34px, 9vw, 46px);
  }

  .topic-hero-meta {
    justify-content: flex-start;
  }

  .timeline-item {
    grid-template-columns: 70px 1fr;
    gap: 16px;
  }

  .timeline-dot {
    left: 70px;
  }

  .search-form {
    flex-direction: column;
  }

  .tutor-input-form {
    flex-direction: column;
  }

  .flashcard-controls {
    flex-direction: column;
  }

  .results-actions {
    flex-direction: column;
    align-items: center;
  }

  .level-selector {
    gap: 3px;
  }

  .level-btn {
    padding: 8px 10px;
    font-size: 12px;
  }

  .topic-card-hero {
    height: 155px;
  }

  .topic-card-body {
    padding: 22px;
  }

  .topic-card-title {
    font-size: 24px;
  }
}

@media (max-width: 480px) {
  .header-actions {
    gap: 5px;
  }

  .btn-icon {
    width: 38px;
    height: 38px;
  }

  .brand {
    font-size: 17px;
  }

  .quick-actions {
    grid-template-columns: 1fr;
  }

  .progress-overview {
    grid-template-columns: repeat(2, 1fr);
  }

  .topic-card-meta {
    gap: 11px;
  }

  .topic-card-hero {
    height: 135px;
  }

  .essential-question {
    padding: 22px;
    font-size: 22px;
  }

  .concept-definition {
    font-size: 18px;
  }

  .tutor-bubble {
    max-width: 88%;
  }

  .fc-stats {
    gap: 20px;
  }
}

@media print {
  .header,
  .footer,
  .btn,
  .quiz-options,
  .tutor-chat,
  .flashcard-controls,
  .flashcard-rate {
    display: none;
  }

  .main {
    padding-top: 0;
  }

  body {
    background: white;
    color: black;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: .01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: .01ms !important;
    scroll-behavior: auto !important;
  }
}

::-webkit-scrollbar {
  width: 8px;
}

::-webkit-scrollbar-track {
  background: var(--canvas);
}

::-webkit-scrollbar-thumb {
  background: var(--keyline-strong);
  border-radius: 999px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--text-muted);
}

.header {
  position: fixed;
  top: 16px;
  left: 50%;
  right: auto;
  width: min(calc(100% - 32px), 1160px);
  height: 64px;
  transform: translateX(-50%);
  border: 1px solid var(--keyline);
  border-radius: 18px;
  background: var(--surface-acrylic);
  box-shadow: var(--shadow-md);
}

.header-inner {
  max-width: none;
  padding: 0 20px;
}

.brand {
  font-size: 18px;
  letter-spacing: .01em;
}

.brand-icon {
  width: 22px;
  height: 22px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-size: 19px;
}

.nav {
  gap: 28px;
}

.nav-link {
  padding: 22px 2px 20px;
  font-size: 13px;
}

.header-actions {
  gap: 7px;
}

.btn-icon {
  width: 40px;
  height: 40px;
  border-radius: 50%;
  background: transparent;
}

.btn-icon:hover {
  background: var(--surface);
  transform: translateY(-1px);
}

.theme-icon-dark,
[data-theme="dark"] .theme-icon-light {
  display: none;
}

[data-theme="dark"] .theme-icon-dark {
  display: inline-flex;
}

.mobile-menu {
  display: none;
  position: relative;
}

.mobile-menu summary {
  list-style: none;
  cursor: pointer;
}

.mobile-menu summary::-webkit-details-marker {
  display: none;
}

.mobile-nav {
  position: absolute;
  top: 48px;
  right: 0;
  min-width: 170px;
  padding: 8px;
  border: 1px solid var(--keyline);
  border-radius: 14px;
  background: var(--card-bg);
  box-shadow: var(--shadow-lg);
}

.mobile-nav a {
  display: block;
  padding: 10px 12px;
  border-radius: 9px;
  color: var(--text-secondary);
  font-size: 14px;
}

.mobile-nav a:hover,
.mobile-nav a.active {
  color: var(--text-primary);
  background: var(--accent-bg);
}

.main {
  padding-top: 96px;
}

.discover-page {
  background:
    radial-gradient(circle at 7% 14%, var(--accent-bg), transparent 24%),
    var(--canvas);
}

.discover-shell {
  position: relative;
  width: min(calc(100% - 32px), 1160px);
  margin: 0 auto;
  overflow: hidden;
  border: 1px solid var(--keyline);
  border-radius: 22px;
  background: var(--canvas-elevated);
  box-shadow: var(--shadow-lg);
}

.discover-shell::before,
.discover-shell::after {
  content: "";
  position: absolute;
  pointer-events: none;
  border: 1px solid var(--keyline);
  border-radius: 50%;
  opacity: .45;
}

.discover-shell::before {
  width: 250px;
  height: 250px;
  left: -145px;
  bottom: -120px;
}

.discover-shell::after {
  width: 360px;
  height: 360px;
  right: -210px;
  top: -220px;
}

.discover-topbar {
  min-height: 48px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
  padding: 0 28px;
  border-bottom: 1px solid var(--keyline);
  color: var(--text-muted);
  font-size: 10px;
  letter-spacing: .12em;
  text-transform: uppercase;
}

.discover-kicker {
  color: var(--text-secondary);
  font-weight: 750;
}

.discover-note {
  letter-spacing: .03em;
  text-transform: none;
}

.discover-layout {
  display: grid;
  grid-template-columns: minmax(230px, .7fr) minmax(0, 1.7fr);
  gap: 28px;
  padding: 38px 28px 30px;
}

.discover-intro {
  position: relative;
  z-index: 1;
  padding: 10px 0 18px;
}

.discover-eyebrow {
  margin-bottom: 12px;
  color: var(--accent);
  font-size: 10px;
  font-weight: 750;
  letter-spacing: .14em;
  text-transform: uppercase;
}

.discover-title {
  max-width: 320px;
  margin-bottom: 18px;
  font-family: var(--font-serif);
  font-size: clamp(40px, 4.4vw, 58px);
  font-weight: 600;
  line-height: .98;
  letter-spacing: -.045em;
}

.discover-description {
  max-width: 290px;
  color: var(--text-secondary);
  font-size: 14px;
  line-height: 1.7;
}

.discover-rule {
  display: block;
  width: 26px;
  height: 1px;
  margin: 22px 0 18px;
  background: var(--accent);
}

.discover-microcopy {
  max-width: 255px;
  color: var(--text-muted);
  font-size: 11px;
  line-height: 1.65;
}

.discover-link {
  display: inline-flex;
  gap: 8px;
  align-items: center;
  margin-top: 22px;
  color: var(--accent);
  font-size: 12px;
  font-weight: 650;
}

.discover-link:hover {
  color: var(--accent-strong);
  transform: translateX(2px);
}

.discover-featured {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 16px;
}

.featured-topic-card {
  position: relative;
  display: flex;
  flex-direction: column;
  min-width: 0;
  overflow: hidden;
  color: var(--text-primary);
  border: 1px solid var(--keyline);
  border-radius: 16px;
  background: var(--card-bg);
  box-shadow: var(--shadow-sm);
  transition: transform var(--transition-med), box-shadow var(--transition-med), border-color var(--transition-med);
}

.featured-topic-card:hover {
  color: var(--text-primary);
  transform: translateY(-3px);
  border-color: var(--keyline-strong);
  box-shadow: var(--shadow-lg);
}

.featured-topic-art {
  position: relative;
  height: 150px;
  overflow: hidden;
  display: flex;
  align-items: center;
  justify-content: center;
  border-bottom: 1px solid var(--keyline);
  background:
    radial-gradient(circle at 50% 55%, var(--accent-bg), transparent 45%),
    linear-gradient(135deg, var(--surface), var(--canvas-elevated));
}

.featured-topic-card-2 .featured-topic-art {
  background:
    radial-gradient(circle at 45% 48%, var(--amber-bg), transparent 35%),
    linear-gradient(135deg, var(--surface), var(--canvas-elevated));
}

.featured-topic-symbol {
  position: relative;
  z-index: 2;
  font-size: 62px;
  line-height: 1;
  filter: drop-shadow(0 8px 14px var(--glow));
}

.featured-topic-card-1 .featured-topic-symbol {
  width: 78px;
  height: 78px;
  border-radius: 50%;
  font-size: 0;
  background: #07090b;
  box-shadow:
    0 0 0 7px rgba(184,102,25,.08),
    0 0 0 13px rgba(184,102,25,.18),
    0 0 28px rgba(184,102,25,.38);
}

.featured-topic-card-1 .featured-topic-symbol::before {
  content: "";
  position: absolute;
  inset: -13px;
  border: 5px solid var(--accent);
  border-left-color: transparent;
  border-right-color: rgba(184,102,25,.35);
  border-radius: 50%;
  transform: rotate(-14deg) skewX(-8deg);
  filter: blur(.2px);
}

.featured-topic-card-2 .featured-topic-symbol {
  font-size: 66px;
  filter: drop-shadow(0 10px 14px rgba(80,55,20,.18));
}

.featured-topic-orbit {
  position: absolute;
  width: 145px;
  height: 48px;
  border: 1px solid var(--keyline-strong);
  border-radius: 50%;
  transform: rotate(-14deg);
  opacity: .75;
}

.featured-topic-card-2 .orbit-one {
  width: 180px;
  transform: rotate(-14deg);
}

.featured-topic-card-2 .orbit-two {
  width: 120px;
  transform: rotate(25deg);
  opacity: .4;
}

.featured-topic-card-1 .featured-topic-orbit {
  width: 185px;
  transform: rotate(-18deg);
  opacity: .2;
}

.featured-topic-body {
  padding: 20px 20px 17px;
}

.featured-topic-body h2 {
  margin: 0 0 7px;
  font-family: var(--font-serif);
  font-size: 23px;
  font-weight: 600;
  line-height: 1.15;
  letter-spacing: -.025em;
}

.featured-topic-body p {
  margin-bottom: 17px;
  color: var(--text-secondary);
  font-size: 13px;
}

.featured-topic-meta {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 8px 14px;
  padding-top: 13px;
  border-top: 1px solid var(--keyline);
  color: var(--text-muted);
  font-size: 10px;
}

.featured-topic-meta span:first-child {
  color: var(--accent);
}

.discover-support {
  width: min(calc(100% - 32px), 1160px);
  margin: 28px auto 0;
  padding-top: 24px;
}

.discover-support .container {
  padding: 0;
}

.discover-support .feature-grid {
  border-radius: 16px;
  overflow: hidden;
}

@media (max-width: 900px) {
  .discover-layout {
    grid-template-columns: 1fr;
  }

  .discover-intro {
    padding-bottom: 0;
  }

  .discover-title,
  .discover-description,
  .discover-microcopy {
    max-width: 520px;
  }
}

@media (max-width: 680px) {
  .header {
    top: 10px;
    width: calc(100% - 20px);
    height: 58px;
    border-radius: 16px;
  }

  .header-inner {
    padding: 0 12px;
  }

  .nav {
    display: none;
  }

  .mobile-menu {
    display: block;
  }

  .header-actions {
    margin-left: auto;
  }

  .main {
    padding-top: 82px;
  }

  .discover-shell,
  .discover-support {
    width: calc(100% - 20px);
  }

  .discover-topbar {
    align-items: flex-start;
    flex-direction: column;
    gap: 4px;
    padding: 13px 18px;
  }

  .discover-layout {
    gap: 24px;
    padding: 28px 18px 20px;
  }

  .discover-title {
    font-size: clamp(42px, 13vw, 56px);
  }

  .discover-featured {
    grid-template-columns: 1fr;
  }

  .featured-topic-art {
    height: 145px;
  }
}

@media (max-width: 430px) {
  .brand {
    font-size: 16px;
  }

  .brand-icon {
    width: 19px;
    height: 19px;
    font-size: 17px;
  }

  .header-actions .btn-icon {
    width: 36px;
    height: 36px;
  }

  .discover-title {
    font-size: 43px;
  }
}



.discover-decor {
  position: absolute;
  inset: 0;
  pointer-events: none;
  z-index: 0;
  overflow: hidden;
}

.discover-decor-leaves {
  display: block;
}

.leaf-stem {
  position: absolute;
  left: 34px;
  bottom: -12px;
  width: 1px;
  height: 310px;
  background: linear-gradient(to top, transparent, var(--keyline-strong));
  transform: rotate(-20deg);
  transform-origin: bottom center;
  opacity: .7;
}

.leaf {
  position: absolute;
  left: 22px;
  width: 22px;
  height: 54px;
  border: 1px solid var(--keyline-strong);
  border-radius: 100% 0 100% 0;
  background: linear-gradient(145deg, var(--surface-strong), var(--card-bg));
  opacity: .82;
  transform-origin: bottom right;
}

.leaf::after {
  content: "";
  position: absolute;
  left: 50%;
  top: 7px;
  width: 1px;
  height: 42px;
  background: var(--keyline-strong);
  transform: rotate(18deg);
  transform-origin: top center;
  opacity: .65;
}

.leaf-1 { top: 126px; transform: rotate(-33deg); }
.leaf-2 { top: 184px; transform: rotate(-55deg) scale(.82); }
.leaf-3 { top: 238px; transform: rotate(-22deg) scale(.9); }
.leaf-4 { top: 296px; transform: rotate(-58deg) scale(.72); }
.leaf-5 { top: 340px; transform: rotate(-20deg) scale(.62); }

.discover-decor-stars {
  display: none;
}

.star {
  position: absolute;
  width: 4px;
  height: 4px;
  border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 0 10px var(--glow);
  opacity: .8;
}

.star::before,
.star::after {
  content: "";
  position: absolute;
  left: 50%;
  top: 50%;
  width: 14px;
  height: 1px;
  background: currentColor;
  transform: translate(-50%, -50%);
  opacity: .45;
}

.star::after {
  transform: translate(-50%, -50%) rotate(90deg);
}

.star-1 { top: 18%; right: 8%; color: var(--accent); }
.star-2 { top: 30%; right: 23%; width: 3px; height: 3px; color: var(--mint); }
.star-3 { top: 66%; right: 9%; width: 3px; height: 3px; color: var(--violet); }
.star-4 { top: 78%; right: 31%; width: 2px; height: 2px; color: var(--amber); }
.star-5 { top: 14%; right: 36%; width: 2px; height: 2px; color: var(--mint); }

.orbit-line {
  position: absolute;
  border: 1px solid var(--keyline);
  border-radius: 50%;
  opacity: .5;
}

.orbit-line-1 {
  width: 340px;
  height: 105px;
  right: -80px;
  top: 52px;
  transform: rotate(-16deg);
}

.orbit-line-2 {
  width: 430px;
  height: 145px;
  right: -130px;
  bottom: 25px;
  transform: rotate(13deg);
  opacity: .28;
}

@media (max-width: 900px) {
  .leaf-stem { left: 22px; }
  .leaf { left: 13px; }
}

@media (max-width: 680px) {
  .discover-decor-leaves { opacity: .55; }
  .leaf-stem { height: 230px; }
  .leaf-1 { top: 145px; }
  .leaf-2 { top: 195px; }
  .leaf-3 { top: 245px; }
  .leaf-4 { top: 292px; }
  .leaf-5 { top: 330px; }
}


[data-theme="light"] .discover-page {
  background:
    radial-gradient(circle at 8% 20%, rgba(184,102,25,.06), transparent 22%),
    radial-gradient(circle at 92% 78%, rgba(85,123,104,.055), transparent 24%),
    var(--canvas);
}

[data-theme="light"] .discover-shell::before {
  box-shadow: inset 0 0 0 1px rgba(184,102,25,.025);
}


[data-theme="dark"] .discover-decor-leaves {
  display: none;
}

[data-theme="dark"] .discover-decor-stars {
  display: block;
}

[data-theme="dark"] .discover-page {
  background:
    radial-gradient(circle at 17% 14%, rgba(156,139,255,.11), transparent 23%),
    radial-gradient(circle at 84% 68%, rgba(54,197,200,.075), transparent 25%),
    radial-gradient(circle at 52% 30%, rgba(255,255,255,.025) 0 1px, transparent 1.5px),
    radial-gradient(circle at 78% 18%, rgba(255,255,255,.035) 0 1px, transparent 1.5px),
    radial-gradient(circle at 28% 76%, rgba(255,255,255,.028) 0 1px, transparent 1.5px),
    var(--canvas);
}

[data-theme="dark"] .discover-shell {
  background:
    radial-gradient(circle at 52% 8%, rgba(156,139,255,.055), transparent 28%),
    linear-gradient(180deg, rgba(13,26,41,.98), rgba(7,17,28,.98));
  box-shadow: 0 22px 70px rgba(0,0,0,.34), inset 0 1px 0 rgba(255,255,255,.025);
}

[data-theme="dark"] .featured-topic-art {
  background:
    radial-gradient(circle at 50% 52%, rgba(156,139,255,.13), transparent 38%),
    radial-gradient(circle at 30% 30%, rgba(255,255,255,.035) 0 1px, transparent 1.5px),
    radial-gradient(circle at 74% 70%, rgba(255,255,255,.03) 0 1px, transparent 1.5px),
    #0a1624;
}

[data-theme="dark"] .featured-topic-card-2 .featured-topic-art {
  background:
    radial-gradient(circle at 48% 48%, rgba(54,197,200,.10), transparent 34%),
    radial-gradient(circle at 22% 26%, rgba(255,255,255,.035) 0 1px, transparent 1.5px),
    radial-gradient(circle at 78% 72%, rgba(255,255,255,.03) 0 1px, transparent 1.5px),
    #0a1624;
}

[data-theme="dark"] .featured-topic-card-1 .featured-topic-symbol {
  background: #02070d;
  box-shadow:
    0 0 0 7px rgba(156,139,255,.08),
    0 0 0 13px rgba(156,139,255,.12),
    0 0 34px rgba(156,139,255,.32);
}

[data-theme="dark"] .featured-topic-card-1 .featured-topic-symbol::before {
  border-color: var(--accent);
  border-left-color: transparent;
  border-right-color: rgba(156,139,255,.32);
}

[data-theme="dark"] .discover-topbar,
[data-theme="dark"] .featured-topic-meta {
  border-color: var(--keyline);
}

[data-theme="dark"] .discover-shell::after {
  border-color: rgba(156,139,255,.13);
  box-shadow: 0 0 80px rgba(156,139,255,.035);
}




.discover-shell {
  isolation: isolate;
}

.discover-layout {
  grid-template-columns: minmax(210px, .72fr) minmax(0, 1.75fr) minmax(150px, .48fr);
  align-items: stretch;
}

.discover-intro,
.discover-featured,
.discover-rail {
  position: relative;
  z-index: 2;
}

.discover-featured {
  min-width: 0;
}

.discover-rail {
  display: flex;
  flex-direction: column;
  justify-content: flex-end;
  min-width: 0;
  padding: 14px 0 18px 18px;
  border-left: 1px solid var(--keyline);
}

.discover-rail-mark {
  width: 54px;
  height: 54px;
  margin-bottom: auto;
  position: relative;
  display: grid;
  place-items: center;
  border: 1px solid var(--keyline-strong);
  border-radius: 50%;
  background: var(--surface);
  box-shadow: inset 0 0 0 5px var(--canvas-elevated);
}

.discover-rail-mark::before,
.discover-rail-mark::after {
  content: "";
  position: absolute;
  border: 1px solid var(--keyline);
  border-radius: 50%;
}

.discover-rail-mark::before {
  inset: 7px;
}

.discover-rail-mark::after {
  inset: 14px;
}

.discover-rail-mark span {
  width: 3px;
  height: 3px;
  border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 0 10px var(--glow);
}

.discover-rail-mark span:nth-child(2),
.discover-rail-mark span:nth-child(3) {
  position: absolute;
}

.discover-rail-mark span:nth-child(2) {
  transform: translate(18px, -8px);
  background: var(--mint);
}

.discover-rail-mark span:nth-child(3) {
  transform: translate(-18px, 9px);
  background: var(--violet);
}

.discover-rail-label {
  margin: 34px 0 9px;
  color: var(--accent);
  font-size: 9px;
  font-weight: 800;
  letter-spacing: .16em;
}

.discover-rail-title {
  max-width: 150px;
  margin-bottom: 18px;
  font-family: var(--font-serif);
  font-size: 18px;
  line-height: 1.15;
  letter-spacing: -.02em;
}

.discover-rail-stats {
  display: grid;
  gap: 9px;
  margin-bottom: 16px;
}

.discover-rail-stats > div {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  gap: 8px;
  padding-bottom: 8px;
  border-bottom: 1px solid var(--keyline);
}

.discover-rail-stats strong {
  font-family: var(--font-serif);
  font-size: 18px;
  font-weight: 600;
}

.discover-rail-stats span {
  color: var(--text-muted);
  font-size: 9px;
  text-transform: uppercase;
  letter-spacing: .08em;
}

.discover-rail-line {
  width: 32px;
  height: 1px;
  margin-bottom: 12px;
  background: var(--accent);
}

.discover-rail-note {
  color: var(--text-muted);
  font-size: 10px;
  line-height: 1.6;
}

.discover-intro::before {
  content: "";
  position: absolute;
  left: -18px;
  top: -18px;
  width: 86px;
  height: 86px;
  border: 1px solid var(--keyline);
  border-radius: 50%;
  opacity: .55;
  z-index: -1;
}

.featured-topic-card {
  box-shadow:
    var(--shadow-sm),
    inset 0 0 0 1px rgba(255,255,255,.025);
}

.featured-topic-card::after {
  content: "";
  position: absolute;
  inset: 8px;
  border: 1px solid var(--keyline);
  border-radius: 11px;
  pointer-events: none;
  opacity: .42;
}

.featured-topic-art {
  box-shadow: inset 0 0 0 1px rgba(255,255,255,.02);
}

.featured-topic-art::after {
  content: "";
  position: absolute;
  inset: 12px;
  border: 1px solid var(--keyline);
  border-radius: 10px;
  opacity: .42;
  pointer-events: none;
}

.btn,
.btn-icon,
.search-input,
.tutor-input,
.level-selector,
.feature-card,
.action-card,
.concept-card,
.topic-card,
.results-card,
.flashcard-rate,
.progress-stat {
  box-shadow: inset 0 0 0 1px rgba(255,255,255,.018);
}

.btn-icon {
  position: relative;
  border-radius: 50%;
}

.btn-icon::after {
  content: "";
  position: absolute;
  inset: 4px;
  border: 1px solid var(--keyline);
  border-radius: 50%;
  pointer-events: none;
  opacity: .55;
}

.discover-decor-leaves,
.discover-decor-stars {
  position: absolute;
  inset: 0;
  z-index: 1;
}

.discover-decor-leaves {
  opacity: .9;
}

.discover-decor-leaves::before,
.discover-decor-leaves::after {
  content: "";
  position: absolute;
  border: 1px solid var(--keyline);
  border-radius: 50%;
  pointer-events: none;
}

.discover-decor-leaves::before {
  width: 300px;
  height: 120px;
  left: -175px;
  bottom: 22px;
  transform: rotate(-28deg);
  opacity: .35;
}

.discover-decor-leaves::after {
  width: 190px;
  height: 75px;
  left: -105px;
  top: 92px;
  transform: rotate(22deg);
  opacity: .25;
}

[data-theme="light"] .discover-shell {
  background:
    radial-gradient(circle at 12% 80%, rgba(85,123,104,.055), transparent 25%),
    radial-gradient(circle at 87% 15%, rgba(184,102,25,.045), transparent 24%),
    var(--canvas-elevated);
}

[data-theme="light"] .discover-decor-leaves .leaf {
  background: linear-gradient(145deg, #E7E0D0, #FBF8F2);
  border-color: #C9BCA8;
}

[data-theme="light"] .discover-decor-leaves .leaf::after {
  background: #B8AB96;
}

[data-theme="dark"] .discover-page {
  background:
    radial-gradient(circle at 12% 10%, rgba(156,139,255,.12), transparent 22%),
    radial-gradient(circle at 88% 72%, rgba(54,197,200,.08), transparent 25%),
    var(--canvas);
}

[data-theme="dark"] .discover-shell {
  background:
    radial-gradient(circle at 54% 8%, rgba(156,139,255,.07), transparent 27%),
    linear-gradient(180deg, #0D1A29, #07111C);
  border-color: rgba(170,190,215,.22);
}

[data-theme="dark"] .discover-shell::before,
[data-theme="dark"] .discover-shell::after {
  border-color: rgba(156,139,255,.18);
}

[data-theme="dark"] .discover-decor-stars {
  background:
    radial-gradient(circle at 8% 18%, rgba(255,255,255,.9) 0 1px, transparent 1.6px),
    radial-gradient(circle at 18% 72%, rgba(255,255,255,.65) 0 1px, transparent 1.5px),
    radial-gradient(circle at 35% 28%, rgba(255,255,255,.7) 0 1px, transparent 1.5px),
    radial-gradient(circle at 61% 15%, rgba(255,255,255,.75) 0 1px, transparent 1.5px),
    radial-gradient(circle at 73% 58%, rgba(255,255,255,.6) 0 1px, transparent 1.5px),
    radial-gradient(circle at 91% 32%, rgba(255,255,255,.8) 0 1px, transparent 1.5px);
  opacity: .42;
}

[data-theme="dark"] .discover-rail {
  border-color: rgba(170,190,215,.18);
}

[data-theme="dark"] .discover-rail-mark {
  background: #0A1624;
  box-shadow:
    inset 0 0 0 5px #07111C,
    0 0 30px rgba(156,139,255,.08);
}

[data-theme="dark"] .featured-topic-card {
  background:
    linear-gradient(180deg, rgba(13,26,41,.98), rgba(9,21,34,.98));
  border-color: rgba(170,190,215,.2);
}

[data-theme="dark"] .featured-topic-art {
  background:
    radial-gradient(circle at 50% 50%, rgba(156,139,255,.13), transparent 37%),
    #091522;
}

[data-theme="dark"] .featured-topic-card-2 .featured-topic-art {
  background:
    radial-gradient(circle at 50% 50%, rgba(54,197,200,.11), transparent 35%),
    #091522;
}

[data-theme="dark"] .featured-topic-card::after,
[data-theme="dark"] .featured-topic-art::after {
  border-color: rgba(170,190,215,.17);
}

[data-theme="dark"] .btn-icon::after {
  border-color: rgba(170,190,215,.2);
}

@media (max-width: 1050px) {
  .discover-layout {
    grid-template-columns: minmax(200px, .7fr) minmax(0, 1.7fr);
  }

  .discover-rail {
    grid-column: 1 / -1;
    display: grid;
    grid-template-columns: auto minmax(130px, .7fr) 1fr;
    align-items: center;
    gap: 18px;
    padding: 18px 0 0;
    border-left: 0;
    border-top: 1px solid var(--keyline);
  }

  .discover-rail-mark {
    margin: 0;
  }

  .discover-rail-label {
    margin: 0 0 5px;
  }

  .discover-rail-title {
    margin: 0;
  }

  .discover-rail-stats {
    grid-column: 3;
    grid-row: 1 / span 2;
    grid-template-columns: repeat(3, 1fr);
    margin: 0;
  }

  .discover-rail-note,
  .discover-rail-line {
    display: none;
  }
}

@media (max-width: 900px) {
  .discover-layout {
    grid-template-columns: 1fr;
  }

  .discover-rail {
    grid-column: auto;
    grid-template-columns: auto 1fr;
  }

  .discover-rail-stats {
    grid-column: 1 / -1;
    grid-row: auto;
  }
}

@media (max-width: 680px) {
  .discover-rail {
    grid-template-columns: auto 1fr;
  }

  .discover-rail-stats {
    grid-column: 1 / -1;
  }

  .discover-intro::before {
    left: -35px;
    top: -22px;
  }
}



.global-theme-atmosphere {
  position: fixed;
  inset: 0;
  width: 100%;
  height: 100%;
  pointer-events: none;
  overflow: hidden;
  z-index: 0;
}


.app-shell {
  position: relative;
  z-index: 1;
}



.global-theme-leaves {
  position: absolute;
  inset: 0;
  pointer-events: none;
  overflow: hidden;
  opacity: 1;
}

.global-leaf-stem {
  position: absolute;
  left: 28px;
  top: 18%;
  width: 1px;
  height: 420px;
  background: linear-gradient(
    to bottom,
    transparent,
    var(--keyline-strong),
    transparent
  );
  transform: rotate(-18deg);
  transform-origin: top center;
  opacity: .65;
}

.global-leaf {
  position: absolute;
  left: 18px;
  width: 30px;
  height: 72px;
  border: 1px solid var(--keyline-strong);
  border-radius: 100% 0 100% 0;
  background: linear-gradient(
    145deg,
    var(--surface-strong),
    var(--card-bg)
  );
  opacity: .7;
  transform-origin: bottom right;
}

.global-leaf::after {
  content: "";
  position: absolute;
  left: 50%;
  top: 7px;
  width: 1px;
  height: 56px;
  background: var(--keyline-strong);
  transform: rotate(18deg);
  transform-origin: top center;
  opacity: .7;
}

.global-leaf-1 {
  top: 18%;
  transform: rotate(-30deg);
}

.global-leaf-2 {
  top: 28%;
  transform: rotate(-54deg) scale(.84);
}

.global-leaf-3 {
  top: 38%;
  transform: rotate(-20deg) scale(.92);
}

.global-leaf-4 {
  top: 48%;
  transform: rotate(-56deg) scale(.76);
}

.global-leaf-5 {
  top: 57%;
  transform: rotate(-18deg) scale(.64);
}



.global-theme-stars {
  position: absolute;
  inset: 0;
  pointer-events: none;
  overflow: hidden;
  opacity: 0;
}

.global-star {
  position: absolute;
  width: 4px;
  height: 4px;
  border-radius: 50%;
  background: var(--accent);
  box-shadow: 0 0 14px var(--glow);
  opacity: .8;
}

.global-star::before,
.global-star::after {
  content: "";
  position: absolute;
  left: 50%;
  top: 50%;
  width: 18px;
  height: 1px;
  background: currentColor;
  transform: translate(-50%, -50%);
  opacity: .45;
}

.global-star::after {
  transform: translate(-50%, -50%) rotate(90deg);
}

.global-star-1 {
  top: 13%;
  right: 9%;
  color: var(--accent);
}

.global-star-2 {
  top: 31%;
  right: 23%;
  width: 3px;
  height: 3px;
  color: var(--mint);
}

.global-star-3 {
  top: 58%;
  right: 8%;
  width: 3px;
  height: 3px;
  color: var(--violet);
}

.global-star-4 {
  top: 76%;
  right: 31%;
  width: 2px;
  height: 2px;
  color: var(--amber);
}

.global-star-5 {
  top: 18%;
  right: 37%;
  width: 2px;
  height: 2px;
  color: var(--mint);
}



.global-orbit {
  position: absolute;
  border: 1px solid var(--keyline);
  border-radius: 50%;
  pointer-events: none;
  opacity: .35;
}

.global-orbit-1 {
  width: 620px;
  height: 190px;
  right: -190px;
  top: 10%;
  transform: rotate(-15deg);
}

.global-orbit-2 {
  width: 780px;
  height: 250px;
  left: -300px;
  top: 48%;
  transform: rotate(12deg);
  opacity: .2;
}

.global-orbit-3 {
  width: 520px;
  height: 170px;
  right: -170px;
  bottom: 8%;
  transform: rotate(17deg);
  opacity: .22;
}



.global-theme-glow {
  position: absolute;
  width: 520px;
  height: 520px;
  border-radius: 50%;
  pointer-events: none;
  filter: blur(10px);
  opacity: .28;
}

.global-theme-glow-1 {
  left: -260px;
  top: 18%;
  background: radial-gradient(
    circle,
    var(--glow),
    transparent 68%
  );
}

.global-theme-glow-2 {
  right: -260px;
  bottom: 12%;
  background: radial-gradient(
    circle,
    var(--glow),
    transparent 68%
  );
}



[data-theme="light"] .global-theme-leaves {
  opacity: 1;
}

[data-theme="light"] .global-theme-stars {
  opacity: 0;
}

[data-theme="dark"] .global-theme-leaves {
  opacity: 0;
}

[data-theme="dark"] .global-theme-stars {
  opacity: 1;
}



[data-theme="light"] body {
  background: var(--canvas);
}

[data-theme="dark"] body {
  background: var(--canvas);
}


.global-theme-atmosphere,
.global-theme-atmosphere * {
  pointer-events: none;
}


@media (max-width: 700px) {
  .global-theme-leaves {
    opacity: .65;
  }

  .global-leaf-stem {
    left: 12px;
    height: 300px;
  }

  .global-leaf {
    left: 5px;
    width: 23px;
    height: 58px;
  }

  .global-orbit-1 {
    right: -320px;
  }

  .global-orbit-2 {
    left: -420px;
  }

  .global-orbit-3 {
    right: -300px;
  }
}




.feature-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 16px;
  border: 0;
}

.feature-card {
  position: relative;
  min-height: 190px;
  overflow: hidden;
  padding: 30px 26px;

  background: var(--card-bg);
  border: 1px solid var(--keyline);
  border-radius: 18px;

  box-shadow:
    var(--shadow-sm),
    inset 0 0 0 1px rgba(255,255,255,.018);

  cursor: default;

  transition:
    transform 240ms cubic-bezier(.2,.8,.2,1),
    border-color 220ms ease,
    background 220ms ease,
    box-shadow 240ms cubic-bezier(.2,.8,.2,1);
}


.feature-card::before {
  content: "";
  position: absolute;
  inset: 0;
  z-index: 0;
  pointer-events: none;
  border-radius: inherit;

  background: linear-gradient(
    115deg,
    transparent 25%,
    rgba(255,255,255,.10) 48%,
    transparent 70%
  );

  transform: translateX(-120%);
  opacity: 0;
  transition:
    transform 520ms cubic-bezier(.2,.7,.2,1),
    opacity 180ms ease;
}


.feature-card::after {
  content: "";
  position: absolute;
  inset: 8px;
  z-index: 0;
  pointer-events: none;
  border: 1px solid var(--keyline);
  border-radius: 12px;
  opacity: .35;
  transition:
    opacity 220ms ease,
    border-color 220ms ease,
    inset 220ms ease;
}

.feature-card:hover {
  background: var(--card-hover);
  border-color: var(--keyline-strong);
  transform: translateY(-5px);
  box-shadow:
    var(--shadow-md),
    inset 0 0 0 1px rgba(255,255,255,.022);
}

.feature-card:hover::before {
  opacity: .7;
  transform: translateX(120%);
}

.feature-card:hover::after {
  inset: 7px;
  opacity: .6;
  border-color: var(--keyline-strong);
}

.feature-card:active {
  transform: translateY(-1px) scale(.985);
  box-shadow: var(--shadow-sm);
}

.feature-icon,
.feature-card h3,
.feature-card p {
  position: relative;
  z-index: 1;
}

.feature-icon {
  transition: transform 220ms cubic-bezier(.2,.8,.2,1);
}

.feature-card:hover .feature-icon {
  transform: translateY(-3px) scale(1.06);
}



.btn {
  position: relative;
  overflow: hidden;
  isolation: isolate;
  border-radius: 11px;
  transition:
    background 180ms ease,
    border-color 180ms ease,
    color 180ms ease,
    transform 180ms cubic-bezier(.2,.8,.2,1),
    box-shadow 180ms ease;
}


.btn::before {
  content: "";
  position: absolute;
  inset: 0;
  z-index: -1;
  pointer-events: none;

  background: linear-gradient(
    110deg,
    transparent 24%,
    rgba(255,255,255,.16) 50%,
    transparent 76%
  );

  transform: translateX(-125%);
  transition: transform 460ms cubic-bezier(.2,.7,.2,1);
}

.btn:hover {
  transform: translateY(-2px);
}

.btn:hover::before {
  transform: translateX(125%);
}

.btn:active {
  transform: translateY(1px) scale(.975);
  box-shadow: none;
}

.btn:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 3px;
}

.btn-primary:hover {
  box-shadow: var(--shadow-md);
}

.btn-outline:hover {
  box-shadow: var(--shadow-sm);
}



.btn-icon {
  position: relative;
  overflow: hidden;
  transition:
    transform 180ms cubic-bezier(.2,.8,.2,1),
    background 180ms ease,
    border-color 180ms ease,
    color 180ms ease,
    box-shadow 180ms ease;
}

.btn-icon::before {
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
  border-radius: inherit;
  background: linear-gradient(
    120deg,
    transparent 28%,
    rgba(255,255,255,.12) 50%,
    transparent 72%
  );
  transform: translateX(-125%);
  transition: transform 420ms cubic-bezier(.2,.7,.2,1);
}

.btn-icon:hover {
  transform: translateY(-2px) scale(1.02);
  box-shadow: var(--shadow-sm);
}

.btn-icon:hover::before {
  transform: translateX(125%);
}

.btn-icon:active {
  transform: translateY(1px) scale(.94);
  box-shadow: none;
}



.topic-card,
.featured-topic-card,
.concept-card,
.action-card,
.rate-btn,
.quiz-option,
.quiz-option-lg {
  transition:
    transform 220ms cubic-bezier(.2,.8,.2,1),
    border-color 200ms ease,
    background 200ms ease,
    box-shadow 220ms cubic-bezier(.2,.8,.2,1),
    color 180ms ease;
}

.topic-card:hover,
.featured-topic-card:hover,
.concept-card:hover {
  transform: translateY(-4px);
}

.topic-card:active,
.featured-topic-card:active,
.concept-card:active {
  transform: translateY(-1px) scale(.99);
}

.action-card:hover,
.rate-btn:hover,
.quiz-option:hover,
.quiz-option-lg:hover:not(.answered) {
  transform: translateY(-2px);
}

.action-card:active,
.rate-btn:active,
.quiz-option:active,
.quiz-option-lg:active {
  transform: translateY(1px) scale(.99);
}



.nav-link,
.discover-link,
.back-link,
.lib-tab,
.chip {
  transition:
    color 160ms ease,
    border-color 160ms ease,
    background 160ms ease,
    transform 160ms cubic-bezier(.2,.8,.2,1);
}

.nav-link:hover,
.discover-link:hover,
.back-link:hover,
.lib-tab:hover,
.chip:hover {
  transform: translateY(-1px);
}



.global-theme-leaves .global-leaf {
  transition: transform 700ms cubic-bezier(.2,.7,.2,1), opacity 400ms ease;
}

.global-theme-leaves .global-leaf-1 {
  animation: encartaLeafFloatOne 8s ease-in-out infinite;
}

.global-theme-leaves .global-leaf-2 {
  animation: encartaLeafFloatTwo 10s ease-in-out infinite;
}

.global-theme-leaves .global-leaf-3 {
  animation: encartaLeafFloatThree 9s ease-in-out infinite;
}

.global-theme-leaves .global-leaf-4 {
  animation: encartaLeafFloatTwo 11s ease-in-out infinite reverse;
}

.global-theme-stars .global-star-1,
.global-theme-stars .global-star-3 {
  animation: encartaStarPulse 4.5s ease-in-out infinite;
}

.global-theme-stars .global-star-2,
.global-theme-stars .global-star-5 {
  animation: encartaStarPulse 6s ease-in-out infinite 1s;
}

.global-theme-stars .global-star-4 {
  animation: encartaStarPulse 5.2s ease-in-out infinite 1.8s;
}

@keyframes encartaLeafFloatOne {
  0%, 100% { transform: rotate(-30deg) translate3d(0,0,0); }
  50% { transform: rotate(-27deg) translate3d(2px,-4px,0); }
}

@keyframes encartaLeafFloatTwo {
  0%, 100% { transform: rotate(-54deg) scale(.84) translate3d(0,0,0); }
  50% { transform: rotate(-51deg) scale(.84) translate3d(2px,-3px,0); }
}

@keyframes encartaLeafFloatThree {
  0%, 100% { transform: rotate(-20deg) scale(.92) translate3d(0,0,0); }
  50% { transform: rotate(-18deg) scale(.92) translate3d(2px,-4px,0); }
}

@keyframes encartaStarPulse {
  0%, 100% { opacity: .45; transform: scale(.9); }
  50% { opacity: 1; transform: scale(1.15); }
}



@media (max-width: 960px) {
  .feature-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 14px;
    border: 0;
  }
}

@media (max-width: 768px) {
  .feature-grid {
    grid-template-columns: 1fr;
    gap: 14px;
  }

  .feature-card {
    min-height: 175px;
    padding: 26px 22px;
  }
}

@media (max-width: 480px) {
  .feature-card {
    min-height: 160px;
    padding: 24px 20px;
    border-radius: 16px;
  }
}



@media (prefers-reduced-motion: reduce) {
  .feature-card,
  .feature-card::before,
  .feature-card::after,
  .btn,
  .btn::before,
  .btn-icon,
  .btn-icon::before,
  .topic-card,
  .featured-topic-card,
  .concept-card,
  .action-card,
  .rate-btn,
  .quiz-option,
  .quiz-option-lg,
  .nav-link,
  .discover-link,
  .back-link,
  .lib-tab,
  .chip,
  .global-theme-leaves .global-leaf,
  .global-theme-stars .global-star {
    animation: none !important;
    transition: none !important;
  }
}