:root {
  --bg: #f3efff;
  --bg-deep: #e9e4ff;
  --card: rgba(252, 249, 255, 0.9);
  --card-strong: rgba(255, 255, 255, 0.96);
  --ink: #20184a;
  --muted: #6a6099;
  --line: rgba(83, 65, 159, 0.16);
  --accent: #5d46db;
  --accent-soft: rgba(93, 70, 219, 0.12);
  --accent-strong: #3f30aa;
  --rose: #d83e66;
  --rose-soft: rgba(216, 62, 102, 0.12);
  --blue: #2d68ed;
  --blue-soft: rgba(45, 104, 237, 0.12);
  --shadow: 0 22px 55px rgba(55, 42, 125, 0.14);
  --radius-xl: 28px;
  --radius-lg: 22px;
  --radius-md: 16px;
}

* {
  box-sizing: border-box;
}

html {
  background:
    radial-gradient(circle at top left, rgba(216, 62, 102, 0.18), transparent 28%),
    radial-gradient(circle at top right, rgba(45, 104, 237, 0.18), transparent 28%),
    radial-gradient(circle at bottom center, rgba(93, 70, 219, 0.14), transparent 32%),
    linear-gradient(180deg, var(--bg) 0%, var(--bg-deep) 100%);
}

body {
  margin: 0;
  color: var(--ink);
  font-family: "Aptos", "Segoe UI Variable", "Trebuchet MS", sans-serif;
  background: transparent;
}

h1,
h2,
h3,
strong {
  font-family: "Iowan Old Style", "Palatino Linotype", "Book Antiqua", Georgia, serif;
}

a {
  color: inherit;
}

code {
  background: rgba(93, 70, 219, 0.1);
  padding: 0.08rem 0.36rem;
  border-radius: 0.45rem;
}

button {
  font: inherit;
}

.hidden {
  display: none !important;
}

.app-shell {
  min-height: 100vh;
  display: grid;
  grid-template-columns: 310px minmax(0, 1fr) 380px;
  gap: 1rem;
  padding: 1rem;
}

.chapter-column,
.main-column,
.side-column {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  min-width: 0;
}

.brand-card,
.chapter-card,
.hero,
.registry-card,
.viewer-card,
.panel {
  background: var(--card);
  border: 1px solid var(--line);
  border-radius: var(--radius-xl);
  box-shadow: var(--shadow);
  backdrop-filter: blur(10px);
}

.brand-card,
.chapter-card,
.hero,
.registry-card,
.panel {
  padding: 1.1rem 1.2rem;
}

.brand-card {
  background: linear-gradient(140deg, rgba(216, 62, 102, 0.97), rgba(93, 70, 219, 0.96) 58%, rgba(45, 104, 237, 0.96));
  color: #fdf8ff;
}

.brand-card .eyebrow,
.brand-card p {
  color: rgba(253, 248, 255, 0.85);
}

.brand-card h1 {
  margin: 0.35rem 0 0.55rem;
  font-size: clamp(2rem, 3vw, 2.8rem);
  line-height: 0.95;
  letter-spacing: -0.045em;
}

.eyebrow {
  margin: 0;
  color: var(--accent);
  font-size: 0.76rem;
  font-weight: 800;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.section-heading p:last-child,
.hero-copy p:last-child,
.panel p:last-child {
  color: var(--muted);
}

.chapter-card h2,
.hero h2,
.registry-card h2,
.panel h2 {
  margin: 0.22rem 0 0.55rem;
  letter-spacing: -0.03em;
}

.chapter-list {
  display: grid;
  gap: 0.75rem;
  max-height: calc(100vh - 235px);
  overflow: auto;
  padding-right: 0.1rem;
}

.chapter-button,
.model-button,
.structure-chip,
.choice,
.quiz-actions button {
  border: 1px solid rgba(83, 65, 159, 0.15);
  border-radius: var(--radius-lg);
  background: var(--card-strong);
  cursor: pointer;
  transition: transform 140ms ease, border-color 140ms ease, box-shadow 140ms ease;
}

.chapter-button:hover,
.model-button:hover,
.structure-chip:hover,
.choice:hover,
.quiz-actions button:hover {
  transform: translateY(-1px);
  border-color: rgba(93, 70, 219, 0.35);
}

.chapter-button.active,
.model-button.active,
.structure-chip.active,
.choice.selected {
  border-color: var(--accent);
  outline: 3px solid rgba(93, 70, 219, 0.14);
  box-shadow: 0 12px 30px rgba(93, 70, 219, 0.14);
}

.chapter-button {
  display: grid;
  gap: 0.4rem;
  padding: 1rem;
  text-align: left;
}

.chapter-kicker {
  color: var(--rose);
  font-size: 0.74rem;
  font-weight: 800;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.chapter-copy,
.chapter-stats span,
.model-button span,
.small,
.viewer-meta span {
  color: var(--muted);
}

.chapter-stats,
.hero-stats,
.chapter-goals,
.tag-row,
.structure-list,
.quiz-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.55rem;
}

.chapter-stats span,
.goal-pill,
.tag-chip,
.model-status,
.stat-chip,
.structure-chip {
  border-radius: 999px;
  font-size: 0.8rem;
}

.chapter-stats span,
.goal-pill,
.tag-chip,
.model-status,
.structure-chip {
  padding: 0.34rem 0.62rem;
}

.chapter-stats span,
.tag-chip,
.structure-chip {
  background: rgba(63, 48, 170, 0.08);
}

.hero {
  background: linear-gradient(135deg, rgba(255, 247, 250, 0.94), rgba(241, 238, 255, 0.94) 58%, rgba(240, 246, 255, 0.92));
}

.chapter-hero {
  display: grid;
  gap: 1rem;
}

.hero-stats {
  gap: 0.75rem;
}

.stat-chip {
  min-width: 120px;
  background: rgba(255, 255, 255, 0.74);
  border: 1px solid rgba(83, 65, 159, 0.12);
  padding: 0.85rem 0.9rem;
  display: grid;
  gap: 0.12rem;
}

.stat-chip strong {
  font-size: 1.45rem;
}

.stat-chip span {
  color: var(--muted);
}

.goal-pill {
  background: var(--accent-soft);
  color: var(--accent-strong);
}

.model-list {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 0.7rem;
}

.model-button {
  display: grid;
  gap: 0.26rem;
  padding: 0.9rem;
  text-align: left;
}

.model-button strong,
.model-button span {
  display: block;
}

.model-status {
  width: fit-content;
  background: var(--rose-soft);
  color: #972347;
  margin-top: 0.22rem;
}

.source-link {
  display: inline-flex;
  width: fit-content;
  margin-top: 0.9rem;
  color: var(--accent-strong);
  font-weight: 800;
  text-decoration: none;
}

.viewer-card {
  min-height: 700px;
  position: relative;
  overflow: hidden;
  background:
    radial-gradient(circle at top, rgba(93, 70, 219, 0.2), transparent 30%),
    radial-gradient(circle at bottom right, rgba(45, 104, 237, 0.17), transparent 30%),
    linear-gradient(180deg, rgba(255, 249, 253, 0.9), rgba(240, 236, 255, 0.92));
}

.viewer-meta {
  position: absolute;
  z-index: 2;
  top: 1rem;
  left: 1rem;
  right: 1rem;
  display: flex;
  gap: 0.7rem;
  align-items: center;
  flex-wrap: wrap;
  background: rgba(255, 251, 255, 0.94);
  border: 1px solid rgba(83, 65, 159, 0.12);
  border-radius: 999px;
  padding: 0.62rem 0.95rem;
  box-shadow: 0 12px 30px rgba(0, 0, 0, 0.08);
}

.viewer-surface {
  min-height: 700px;
  padding: 5rem 1rem 6rem;
  display: flex;
  align-items: stretch;
  justify-content: center;
}

.viewer-frame,
.viewer-copy {
  width: 100%;
  max-width: 100%;
}

.viewer-frame {
  border: 0;
  border-radius: 24px;
  min-height: 560px;
  background: rgba(255, 255, 255, 0.7);
}

.viewer-model {
  width: 100%;
  min-height: 560px;
  border-radius: 24px;
  background: rgba(255, 255, 255, 0.6);
}

.viewer-copy {
  border: 1px dashed rgba(83, 65, 159, 0.2);
  border-radius: 24px;
  background: rgba(255, 255, 255, 0.5);
  padding: 1.35rem;
  color: var(--muted);
}

.viewer-copy h3 {
  margin-top: 0;
  color: var(--ink);
}

.warning-note {
  position: absolute;
  left: 1rem;
  right: 1rem;
  bottom: 1rem;
  background: rgba(255, 250, 255, 0.94);
  border: 1px solid rgba(83, 65, 159, 0.12);
  border-radius: var(--radius-lg);
  padding: 0.85rem 1rem;
  color: var(--muted);
}

.structure-list {
  margin-top: 0.9rem;
}

.structure-chip {
  color: var(--accent-strong);
}

.study-prompt,
.feedback {
  margin-top: 1rem;
  padding: 0.95rem 1rem;
  border-radius: var(--radius-lg);
}

.study-prompt {
  background: var(--accent-soft);
}

.choices {
  display: grid;
  gap: 0.55rem;
  margin-top: 0.75rem;
}

.choice,
.quiz-actions button {
  padding: 0.8rem 0.85rem;
  text-align: left;
}

.quiz-actions button {
  text-align: center;
  font-weight: 700;
}

.quiz-actions button:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.feedback.correct {
  background: var(--blue-soft);
}

.feedback.incorrect {
  background: var(--rose-soft);
}

.panel ul {
  padding-left: 1.15rem;
}

@media (max-width: 1260px) {
  .app-shell {
    grid-template-columns: 290px minmax(0, 1fr);
  }

  .side-column {
    grid-column: 1 / -1;
    display: grid;
    grid-template-columns: repeat(2, minmax(0, 1fr));
    align-items: start;
  }
}

@media (max-width: 960px) {
  .app-shell,
  .side-column {
    grid-template-columns: 1fr;
  }

  .chapter-list {
    max-height: none;
  }

  .viewer-card,
  .viewer-surface {
    min-height: 560px;
  }

  .viewer-frame,
  .viewer-model {
    min-height: 440px;
  }
}