:root {
  color-scheme: light;
  --ink: #18212b;
  --muted: #5c6876;
  --paper: #fbfaf7;
  --panel: #ffffff;
  --line: #d9d5ca;
  --accent: #0f766e;
  --accent-2: #b45309;
  --accent-3: #2563eb;
  --soft: #eef4f2;
  --soft-2: #f7efe4;
  --code: #202938;
  --shadow: 0 18px 50px rgba(24, 33, 43, 0.09);
}

* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  color: var(--ink);
  background:
    linear-gradient(90deg, rgba(24, 33, 43, 0.04) 1px, transparent 1px),
    linear-gradient(rgba(24, 33, 43, 0.04) 1px, transparent 1px),
    var(--paper);
  background-size: 28px 28px;
}
a { color: inherit; }
.muted, .card p, .chapter-card p, .lesson-card p, .study-panel p, .lesson-flow p, .goals li { color: var(--muted); }

.mobile-nav-toggle {
  display: none;
  position: fixed;
  right: 1rem;
  bottom: 1rem;
  z-index: 50;
  min-height: 44px;
  padding: 0.75rem 1rem;
  border: 1px solid var(--line);
  border-radius: 999px;
  background: var(--accent);
  color: #fff;
  font-weight: 800;
}

.notebook-layout {
  display: grid;
  grid-template-columns: 300px minmax(0, 1fr);
  min-height: 100vh;
}

.notebook-shell {
  position: sticky;
  top: 0;
  align-self: start;
  height: 100vh;
  overflow: auto;
  padding: 1rem;
  border-right: 1px solid var(--line);
  background: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(14px);
}

.shell-brand {
  display: grid;
  gap: 0.2rem;
  margin-bottom: 1rem;
}
.shell-brand a {
  font-size: 1.3rem;
  font-weight: 900;
  text-decoration: none;
}
.shell-brand span { color: var(--muted); font-size: 0.9rem; }
.shell-actions {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.5rem;
  margin-bottom: 1rem;
}

.shell-nav details {
  border-top: 1px solid var(--line);
  padding: 0.35rem 0;
}
.shell-nav summary {
  display: grid;
  grid-template-columns: 1fr auto;
  gap: 0.5rem;
  align-items: center;
  list-style: none;
  padding: 0.35rem;
  border-radius: 8px;
}
.shell-nav summary::-webkit-details-marker { display: none; }
.shell-nav summary a { text-decoration: none; font-weight: 800; }
.shell-nav summary span {
  display: inline-flex;
  justify-content: center;
  min-width: 1.7rem;
  padding: 0.15rem 0.4rem;
  border-radius: 999px;
  background: var(--soft);
  color: var(--muted);
  font-size: 0.75rem;
}
.shell-nav .active {
  background: var(--soft-2);
  color: var(--accent-2);
}
.lesson-links {
  display: grid;
  gap: 0.25rem;
  padding: 0.35rem 0 0.45rem 0.65rem;
}
.lesson-links a {
  padding: 0.45rem 0.55rem;
  border-radius: 6px;
  color: var(--muted);
  text-decoration: none;
}
.lesson-links a:hover, .lesson-links a.active {
  background: var(--soft);
  color: var(--ink);
}
.shell-current {
  display: grid;
  gap: 0.45rem;
  margin-top: 1rem;
  padding: 0.8rem;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--paper);
  font-size: 0.9rem;
}
.shell-current a { color: var(--accent); text-decoration: none; overflow-wrap: anywhere; }

.notebook-main {
  width: min(1120px, calc(100% - 2rem));
  margin: 0 auto;
  padding: 1rem 0 4rem;
}
.breadcrumbs {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
  align-items: center;
  min-height: 38px;
  color: var(--muted);
  font-size: 0.92rem;
}
.breadcrumbs a { text-decoration: none; color: var(--accent); }

.site-hero, .lesson-hero {
  padding: clamp(2rem, 7vw, 5rem) 0 2rem;
}
.site-hero {
  min-height: 58vh;
  display: grid;
  grid-template-columns: minmax(0, 1.1fr) minmax(280px, 0.9fr);
  align-items: center;
  gap: clamp(2rem, 5vw, 4rem);
}
.site-hero h1, .lesson-hero h1 {
  margin: 0;
  line-height: 0.96;
  letter-spacing: 0;
}
.site-hero h1 { font-size: clamp(3.2rem, 10vw, 7rem); }
.lesson-hero h1 { font-size: clamp(2.4rem, 7vw, 5rem); }
.site-hero p, .lesson-hero p {
  max-width: 820px;
  color: var(--muted);
  font-size: clamp(1.05rem, 2.2vw, 1.35rem);
  line-height: 1.6;
}
.chapter-label {
  margin: 0 0 0.7rem;
  color: var(--accent-2);
  font-size: 0.78rem;
  font-weight: 900;
  letter-spacing: 0;
  text-transform: uppercase;
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 40px;
  padding: 0.65rem 0.9rem;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  text-decoration: none;
  font-weight: 800;
  cursor: pointer;
  color: var(--ink);
}
.button.primary { background: var(--accent); color: #fff; border-color: var(--accent); }
.hero-actions, .card-actions, .lesson-pager { display: flex; flex-wrap: wrap; gap: 0.7rem; margin-top: 1rem; }

.structure-panel, .study-panel, .card, .chapter-card, .lesson-card, .prompt-box, .challenge-box, .theory-block, .lesson-block, .interactive-block, .code-linked, .code-reading-block, .control-panel, .controls-panel {
  border: 1px solid var(--line);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.9);
  box-shadow: var(--shadow);
}
.structure-panel { display: grid; gap: 0.75rem; padding: 1rem; }
.structure-panel div { display: grid; gap: 0.2rem; padding: 0.9rem; border-left: 4px solid var(--accent); background: var(--soft); }

.quick-paths, .cards, .lesson-card-grid, .overview-grid {
  display: grid;
  gap: 1rem;
}
.quick-paths { grid-template-columns: repeat(5, minmax(0, 1fr)); margin: 0 0 2.5rem; }
.quick-paths a, .lesson-card, .card, .chapter-card, .study-panel, .prompt-box, .challenge-box, .theory-block, .lesson-block, .interactive-block, .code-linked, .code-reading-block {
  padding: 1rem;
}
.quick-paths a {
  display: grid;
  gap: 0.35rem;
  min-height: 94px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel);
  text-decoration: none;
}
.quick-paths span { color: var(--muted); font-size: 0.82rem; }
.quick-paths strong { font-size: 1rem; }

.section-heading { margin: 2rem 0 1rem; }
.section-heading h2, .study-panel h2, .lesson-flow h2, .prompt-box h2, .challenge-box h2 { margin: 0 0 0.55rem; font-size: clamp(1.35rem, 2vw, 1.85rem); letter-spacing: 0; }
.cards { grid-template-columns: repeat(3, minmax(0, 1fr)); }
.lesson-card-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
.overview-grid { grid-template-columns: minmax(0, 1.2fr) minmax(280px, 0.8fr); align-items: start; }
.card h3, .chapter-card h3, .lesson-card h3 { margin: 0 0 0.5rem; font-size: 1.15rem; }
.meta { display: flex; flex-wrap: wrap; gap: 0.4rem; margin: 0.8rem 0; }
.tag { display: inline-flex; align-items: center; min-height: 26px; padding: 0.25rem 0.5rem; border: 1px solid var(--line); border-radius: 999px; background: #fff; color: var(--muted); font-size: 0.78rem; }
.goals { margin: 0.75rem 0 0; padding-left: 1.1rem; }
.goals li { margin: 0.25rem 0; }

.lesson-flow {
  display: grid;
  gap: 1.15rem;
  max-width: 1040px;
}
.lesson-block, .interactive-block, .code-reading-block {
  overflow: visible;
}
.interactive-block {
  display: grid;
  grid-template-columns: minmax(0, 1fr) minmax(230px, 0.35fr);
  gap: 1rem;
  align-items: start;
  background: rgba(255, 255, 255, 0.96);
}
.interactive-copy {
  grid-column: 1 / -1;
  display: grid;
  gap: 0.25rem;
}
.interactive-copy h3, .controls-panel h3 {
  margin: 0;
  font-size: 1.1rem;
}
.interactive-copy p, .controls-panel p {
  margin: 0;
  color: var(--muted);
}
.canvas-stage {
  min-width: 0;
  overflow: visible;
}
.inline-demo {
  width: 100%;
  min-height: 280px;
  overflow: visible;
}
.inline-demo canvas {
  display: block;
  width: 100%;
  height: auto;
  max-width: 100%;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: #fff;
}
.controls-panel {
  display: grid;
  gap: 0.8rem;
  padding: 1rem;
  box-shadow: none;
  background: #f7fbfa;
}
.inline-control {
  display: grid;
  gap: 0.35rem;
  margin: 0;
  font-weight: 800;
}
.inline-control-label {
  display: flex;
  justify-content: space-between;
  gap: 0.75rem;
}
.inline-control output {
  color: var(--accent);
  font-variant-numeric: tabular-nums;
}
.inline-control input, .inline-control select, .controls-panel button {
  width: 100%;
}
.control-note {
  font-size: 0.9rem;
}
pre {
  overflow-x: auto;
  overflow-y: visible;
  padding: 1rem;
  border-radius: 8px;
  background: var(--code);
  color: #f7f7f7;
}
.prompt-box { background: #f7fbfa; }
.challenge-box { background: #fff7ed; }
.lesson-pager { padding: 1.25rem 0 0; border-top: 1px solid var(--line); margin-top: 2rem; }

.demo-shell {
  width: min(1100px, calc(100% - 2rem));
  margin: 0 auto;
  padding: 1rem 0 4rem;
}
.demo-grid {
  display: grid;
  grid-template-columns: minmax(320px, 2fr) minmax(260px, 1fr);
  gap: 1.5rem;
  align-items: start;
}
.control-panel { padding: 1rem; box-shadow: none; }
.control-panel label { display: grid; gap: 0.35rem; margin: 0.85rem 0; font-weight: 800; }
.control-panel input, .control-panel select, .control-panel button { width: 100%; }
.control-panel input[type="checkbox"] { width: auto; }
canvas { max-width: 100%; border: 1px solid var(--line); border-radius: 8px; background: #fff; }

@media (max-width: 1050px) {
  .notebook-layout { grid-template-columns: 1fr; }
  .mobile-nav-toggle { display: inline-flex; }
  .notebook-shell {
    position: fixed;
    inset: 0 auto 0 0;
    z-index: 40;
    width: min(340px, 86vw);
    transform: translateX(-105%);
    transition: transform 180ms ease;
  }
  body.nav-open .notebook-shell { transform: translateX(0); }
  .site-hero, .overview-grid, .demo-grid, .interactive-block { grid-template-columns: 1fr; }
  .quick-paths, .cards, .lesson-card-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

@media (max-width: 650px) {
  .quick-paths, .cards, .lesson-card-grid { grid-template-columns: 1fr; }
  .inline-demo { min-height: 240px; }
}