:root {
  --bg: #eef5f3;
  --surface: rgba(255, 255, 255, 0.78);
  --surface-strong: rgba(248, 252, 251, 0.96);
  --surface-dark: #11212e;
  --border: rgba(17, 33, 46, 0.1);
  --border-strong: rgba(17, 33, 46, 0.16);
  --text: #122230;
  --muted: #566b78;
  --accent: #e56e43;
  --accent-2: #1d8c7e;
  --accent-3: #5c7cff;
  --accent-soft: rgba(229, 110, 67, 0.12);
  --shadow: 0 24px 60px rgba(27, 48, 62, 0.08);
  --radius-lg: 28px;
  --radius-md: 18px;
  --radius-sm: 12px;
  --font-display: "DM Sans", "Avenir Next", "Segoe UI", sans-serif;
  --font-body: "DM Sans", "Avenir Next", "Segoe UI", sans-serif;
}

* {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  min-height: 100%;
  background:
    radial-gradient(circle at 10% 10%, rgba(92, 124, 255, 0.12), transparent 22%),
    radial-gradient(circle at 88% 8%, rgba(229, 110, 67, 0.12), transparent 24%),
    radial-gradient(circle at 80% 70%, rgba(29, 140, 126, 0.1), transparent 26%),
    linear-gradient(180deg, #f5fbf8 0%, #edf3f1 46%, #e9f0ee 100%);
  color: var(--text);
  font-family: var(--font-body);
}

body::before {
  content: "";
  position: fixed;
  inset: 0;
  pointer-events: none;
  background:
    linear-gradient(rgba(17, 33, 46, 0.035) 1px, transparent 1px),
    linear-gradient(90deg, rgba(17, 33, 46, 0.035) 1px, transparent 1px);
  background-size: 64px 64px;
  mask-image: linear-gradient(180deg, rgba(0, 0, 0, 0.5), transparent 80%);
  opacity: 0.22;
}

button {
  font: inherit;
}

.app-shell {
  display: grid;
  grid-template-columns: 320px minmax(0, 1fr);
  gap: 24px;
  min-height: 100vh;
  padding: 24px;
}

.sidebar,
.hero-card,
.lesson-main,
.side-card {
  backdrop-filter: blur(18px);
  background: var(--surface);
  border: 1px solid var(--border);
  box-shadow: var(--shadow);
}

.sidebar {
  position: sticky;
  top: 24px;
  align-self: start;
  height: calc(100vh - 48px);
  padding: 24px;
  border-radius: var(--radius-lg);
  overflow: auto;
  background:
    linear-gradient(180deg, rgba(255, 255, 255, 0.92), rgba(246, 251, 249, 0.86)),
    var(--surface);
}

.eyebrow,
.module-label,
.lens-label {
  margin: 0 0 10px;
  color: var(--accent-2);
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0.12em;
  text-transform: uppercase;
}

.sidebar h1,
.hero-card h2,
#lesson-title {
  margin: 0;
  font-family: var(--font-display);
  font-weight: 700;
  letter-spacing: -0.035em;
}

.sidebar h1 {
  font-size: 2rem;
  line-height: 1.02;
}

.sidebar-copy,
#hero-copy,
.lesson-summary,
.side-note,
.rich-text p,
.quiz-block p,
.glossary-detail,
.chip-copy {
  color: var(--muted);
  line-height: 1.6;
}

.sidebar-top {
  position: relative;
  padding-bottom: 18px;
}

.sidebar-top::after {
  content: "";
  position: absolute;
  left: 0;
  right: 0;
  bottom: 0;
  height: 1px;
  background: linear-gradient(90deg, rgba(29, 140, 126, 0.42), transparent);
}

.depth-switcher {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 8px;
  margin: 24px 0;
}

.depth-button,
.ghost-button,
.term-chip,
.toggle-button {
  border-radius: 999px;
  border: 1px solid var(--border);
  background: rgba(255, 255, 255, 0.78);
  color: var(--text);
  cursor: pointer;
  transition: 180ms ease;
}

.depth-button,
.ghost-button {
  padding: 10px 14px;
}

.ghost-button:disabled {
  opacity: 0.42;
  cursor: not-allowed;
  transform: none;
}

.depth-button:hover,
.ghost-button:hover,
.module-button:hover,
.term-chip:hover,
.toggle-button:hover {
  transform: translateY(-1px);
  border-color: rgba(229, 110, 67, 0.36);
  background: rgba(255, 255, 255, 0.96);
}

.depth-button.is-active,
.module-button.is-active,
.term-chip.is-active,
.toggle-button.is-active {
  background: linear-gradient(135deg, rgba(29, 140, 126, 0.14), rgba(92, 124, 255, 0.14));
  color: var(--text);
  border-color: transparent;
  box-shadow: inset 0 0 0 1px rgba(29, 140, 126, 0.12);
}

.module-nav {
  display: grid;
  gap: 10px;
  padding-bottom: 24px;
}

.module-group {
  background: linear-gradient(180deg, rgba(255, 255, 255, 0.82), rgba(245, 250, 248, 0.78));
  border: 1px solid rgba(17, 33, 46, 0.08);
  border-radius: 22px;
  padding: 14px;
}

.module-group h3,
.lesson-section h3,
.side-card h3,
.card h3 {
  margin: 0 0 10px;
  font-size: 1rem;
}

.module-caption {
  margin: 0 0 12px;
  font-size: 0.92rem;
  color: var(--muted);
}

.module-lessons {
  display: grid;
  gap: 8px;
}

.module-button {
  width: 100%;
  text-align: left;
  padding: 12px 14px;
  border-radius: 16px;
  border: 1px solid var(--border);
  background: rgba(255, 255, 255, 0.78);
  cursor: pointer;
}

.module-button.is-complete {
  box-shadow: inset 0 0 0 1px rgba(29, 140, 126, 0.18);
}

.module-button strong,
.term-chip {
  display: block;
}

.module-button-label {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.module-status {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 28px;
  height: 28px;
  padding: 0 8px;
  border-radius: 999px;
  background: rgba(17, 33, 46, 0.08);
  color: var(--muted);
  font-size: 0.8rem;
  font-weight: 700;
}

.module-button.is-complete .module-status {
  background: rgba(29, 140, 126, 0.14);
  color: var(--accent-2);
}

.module-button span {
  display: block;
  margin-top: 4px;
  color: var(--muted);
  font-size: 0.9rem;
}

.content {
  display: grid;
  gap: 24px;
}

.hero-card {
  display: flex;
  justify-content: space-between;
  gap: 24px;
  align-items: end;
  border-radius: var(--radius-lg);
  padding: 24px 28px;
  background:
    radial-gradient(circle at top right, rgba(229, 110, 67, 0.12), transparent 28%),
    radial-gradient(circle at left center, rgba(92, 124, 255, 0.1), transparent 30%),
    linear-gradient(180deg, rgba(255, 255, 255, 0.92), rgba(247, 251, 250, 0.88));
  border: 1px solid var(--border-strong);
}

.hero-card h2 {
  font-size: clamp(2rem, 3vw, 3.4rem);
  line-height: 0.94;
  max-width: 12ch;
}

.hero-card p {
  max-width: 40ch;
}

.hero-meta {
  display: grid;
  gap: 16px;
  min-width: min(380px, 100%);
}

.course-progress {
  display: grid;
  gap: 8px;
}

.progress-copy {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  color: var(--muted);
  font-size: 0.94rem;
}

.progress-copy strong {
  color: var(--text);
}

.progress-track {
  height: 10px;
  border-radius: 999px;
  background: rgba(17, 33, 46, 0.08);
  overflow: hidden;
}

.progress-fill {
  width: 0%;
  height: 100%;
  border-radius: 999px;
  background: linear-gradient(90deg, var(--accent-2), var(--accent-3), var(--accent));
  transition: width 220ms ease;
}

.lesson-frame {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 320px;
  gap: 24px;
}

.lesson-main {
  border-radius: var(--radius-lg);
  padding: 28px;
  background:
    linear-gradient(180deg, rgba(255, 255, 255, 0.88), rgba(247, 251, 250, 0.82));
}

.lesson-header {
  margin-bottom: 20px;
}

#lesson-title {
  font-size: clamp(2rem, 4vw, 3rem);
  line-height: 0.96;
  margin-bottom: 12px;
}

.lesson-actions {
  display: flex;
  gap: 12px;
  margin-bottom: 24px;
}

.lesson-section {
  margin-bottom: 24px;
}

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

.card,
.side-card,
.diagram-shell,
.mermaid-panel {
  background: linear-gradient(180deg, rgba(255, 255, 255, 0.86), rgba(248, 252, 251, 0.82));
  border: 1px solid rgba(17, 33, 46, 0.08);
  border-radius: var(--radius-md);
  padding: 18px;
}

.rich-text p,
.rich-text ul,
.rich-text ol {
  margin: 0 0 12px;
}

.rich-text ul {
  padding-left: 18px;
}

.rich-text li {
  margin-bottom: 8px;
}

.term {
  position: relative;
  border-bottom: 1.5px dashed rgba(29, 140, 126, 0.65);
  cursor: help;
  color: #166f64;
  font-weight: 600;
}

.term::after {
  content: attr(data-short);
  position: absolute;
  left: 0;
  bottom: calc(100% + 8px);
  width: 240px;
  padding: 10px 12px;
  border-radius: 12px;
  background: #11212e;
  color: #f6fbff;
  font-size: 0.88rem;
  line-height: 1.4;
  opacity: 0;
  pointer-events: none;
  transform: translateY(6px);
  transition: 160ms ease;
  box-shadow: 0 16px 30px rgba(16, 34, 45, 0.25);
  z-index: 3;
}

.term:hover::after {
  opacity: 1;
  transform: translateY(0);
}

.term-chips {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
}

.term-chip {
  padding: 12px 14px;
  background: rgba(255, 255, 255, 0.8);
}

.toggle-button {
  padding: 9px 14px;
}

.term-chip small {
  color: inherit;
  opacity: 0.78;
}

.lesson-side {
  display: grid;
  gap: 16px;
  align-content: start;
}

.lens-grid {
  display: grid;
  gap: 18px;
}

.quiz-option {
  display: block;
  width: 100%;
  text-align: left;
  margin-bottom: 10px;
  padding: 12px 14px;
  border-radius: 14px;
  border: 1px solid var(--border);
  background: rgba(255, 255, 255, 0.84);
  color: var(--text);
  cursor: pointer;
}

.quiz-option.is-correct {
  border-color: rgba(47, 108, 100, 0.55);
  background: rgba(47, 108, 100, 0.12);
}

.quiz-option.is-wrong {
  border-color: rgba(191, 90, 54, 0.45);
  background: rgba(191, 90, 54, 0.1);
}

.quiz-feedback {
  margin-top: 12px;
  padding: 12px 14px;
  border-radius: 14px;
  background: rgba(247, 251, 250, 0.92);
}

.mermaid-toolbar {
  display: flex;
  gap: 10px;
  margin-bottom: 12px;
}

.quiz-next {
  margin-top: 12px;
}

.lesson-footer-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 18px;
  padding: 18px 20px;
  border-radius: var(--radius-md);
  border: 1px solid rgba(17, 33, 46, 0.08);
  background: linear-gradient(180deg, rgba(255, 255, 255, 0.86), rgba(244, 249, 247, 0.84));
}

.lesson-status-copy {
  margin: 0;
  color: var(--muted);
}

.complete-button {
  padding: 12px 18px;
  border: 0;
  border-radius: 999px;
  background: linear-gradient(135deg, var(--accent-2), var(--accent-3));
  color: #ffffff;
  font: inherit;
  font-weight: 700;
  cursor: pointer;
  box-shadow: 0 12px 24px rgba(92, 124, 255, 0.16);
}

.complete-button:hover {
  transform: translateY(-1px);
}

.complete-button.is-complete {
  background: linear-gradient(135deg, rgba(29, 140, 126, 0.16), rgba(92, 124, 255, 0.18));
  color: var(--text);
}

.glossary-detail strong {
  display: block;
  color: var(--text);
  margin-bottom: 8px;
}

.diagram-shell {
  overflow: auto;
}

.diagram-flow {
  display: flex;
  align-items: stretch;
  gap: 12px;
  min-width: 620px;
}

.diagram-node {
  flex: 1;
  min-width: 120px;
  padding: 14px;
  border-radius: 18px;
  background:
    linear-gradient(180deg, rgba(255, 255, 255, 0.98), rgba(243, 248, 246, 0.96));
  border: 1px solid rgba(17, 33, 46, 0.1);
}

.diagram-node strong {
  display: block;
  margin-bottom: 6px;
  color: var(--text);
}

.diagram-arrow {
  align-self: center;
  font-size: 1.6rem;
  color: var(--accent);
}

.diagram-note {
  margin-top: 14px;
  color: var(--muted);
}

.compare-grid {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
}

.compare-card {
  border-radius: 18px;
  padding: 14px;
  border: 1px solid rgba(27, 43, 53, 0.1);
}

.compare-card.classic {
  background: linear-gradient(180deg, rgba(29, 140, 126, 0.1), rgba(29, 140, 126, 0.04));
}

.compare-card.ai {
  background: linear-gradient(180deg, rgba(229, 110, 67, 0.12), rgba(229, 110, 67, 0.04));
}

.mermaid-code {
  margin: 0;
  padding: 14px;
  border-radius: 14px;
  background: #11212e;
  color: #e6f1f8;
  overflow: auto;
  border: 1px solid rgba(17, 33, 46, 0.08);
}

.mermaid-render {
  min-height: 220px;
  padding: 8px;
  overflow: auto;
}

.mermaid-render svg {
  max-width: 100%;
  height: auto;
}

@media (max-width: 1100px) {
  .app-shell,
  .lesson-frame {
    grid-template-columns: 1fr;
  }

  .sidebar {
    position: relative;
    top: 0;
    height: auto;
  }

  .lesson-side {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }
}

@media (max-width: 800px) {
  .app-shell {
    padding: 16px;
  }

  .hero-card,
  .lesson-main,
  .sidebar {
    padding: 20px;
  }

  .hero-card,
  .split-grid,
  .lesson-side {
    grid-template-columns: 1fr;
    display: grid;
  }

  .lesson-footer-bar,
  .progress-copy {
    grid-template-columns: 1fr;
    display: grid;
  }

  .diagram-flow,
  .compare-grid {
    min-width: 0;
    grid-template-columns: 1fr;
    display: grid;
  }

  .diagram-arrow {
    justify-self: center;
    transform: rotate(90deg);
  }
}