/* ADHD-friendly: high contrast, short blocks, scannable, no walls of text */
:root {
  --bg: #0f1419;
  --surface: #1a2332;
  --surface-2: #243044;
  --border: #3d4f66;
  --text: #f0f4f8;
  --muted: #9db0c7;
  --accent: #4db8ff;
  --accent-dim: #1e6fa8;
  --ok: #3dd68c;
  --warn: #f5c542;
  --bad: #ff6b6b;
  --radius: 12px;
  --gap: 1rem;
  --max: 42rem;
  font-size: 18px;
}

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

html {
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: system-ui, -apple-system, "Segoe UI", "PingFang SC", "Noto Sans SC", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.5;
  min-height: 100vh;
}

a {
  color: var(--accent);
  text-decoration: none;
}
a:hover { text-decoration: underline; }

.wrap {
  max-width: var(--max);
  margin: 0 auto;
  padding: 1.25rem 1rem 3rem;
}

/* Header */
.site-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--gap);
  padding: 0.75rem 0 1.25rem;
  border-bottom: 2px solid var(--border);
  margin-bottom: 1.5rem;
}
.site-header h1 {
  margin: 0;
  font-size: 1.15rem;
  letter-spacing: 0.02em;
}
.site-header .tag {
  font-size: 0.75rem;
  color: var(--muted);
  background: var(--surface);
  border: 1px solid var(--border);
  padding: 0.2rem 0.55rem;
  border-radius: 999px;
}

/* Nav crumbs */
.crumb {
  font-size: 0.85rem;
  color: var(--muted);
  margin-bottom: 1rem;
}
.crumb a { color: var(--muted); }
.crumb a:hover { color: var(--accent); }

/* Section blocks */
.block {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem 1.1rem;
  margin-bottom: 1rem;
  scroll-margin-top: 1rem;
}
.block h2 {
  margin: 0 0 0.65rem;
  font-size: 0.95rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--accent);
  display: flex;
  align-items: center;
  gap: 0.4rem;
}
.block h2 .num {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 1.4rem;
  height: 1.4rem;
  border-radius: 6px;
  background: var(--accent-dim);
  color: var(--text);
  font-size: 0.75rem;
}

.essence-line {
  font-size: 1.15rem;
  font-weight: 650;
  margin: 0 0 0.4rem;
}
.why {
  margin: 0;
  color: var(--muted);
  font-size: 0.95rem;
}

/* Speak bullets */
.speak-list {
  margin: 0;
  padding-left: 1.2rem;
}
.speak-list li {
  margin-bottom: 0.45rem;
}
.speak-list li:last-child { margin-bottom: 0; }

/* Beautiful Mermaid (not default mermaid.js theme CSS) */
.mermaid-wrap {
  overflow-x: auto;
  background: var(--bg);
  border-radius: 8px;
  padding: 0.75rem;
  border: 1px solid var(--border);
}
.mermaid-wrap .bm-diagram,
.mermaid-wrap .mermaid {
  display: flex;
  justify-content: center;
}
.mermaid-wrap .bm-diagram svg {
  max-width: 100%;
  height: auto;
}
.mermaid-wrap .bm-error {
  color: var(--bad);
  font-size: 0.85rem;
  white-space: pre-wrap;
}
/* Authoring: keep source in <pre class="mermaid"> until /shared/mermaid.js runs */
.mermaid-wrap pre.mermaid {
  margin: 0;
  white-space: pre-wrap;
  font-size: 0.8rem;
  color: var(--muted);
}

/* Motion placeholder */
.motion-stage {
  background: var(--bg);
  border: 1px dashed var(--border);
  border-radius: 8px;
  padding: 1rem;
  min-height: 140px;
  position: relative;
  overflow: hidden;
}
.motion-hint {
  font-size: 0.8rem;
  color: var(--muted);
  margin: 0 0 0.75rem;
}
.timeline {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  align-items: center;
}
.tl-node {
  background: var(--surface-2);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.45rem 0.7rem;
  font-size: 0.85rem;
  opacity: 0.35;
  transition: opacity 0.3s, border-color 0.3s, transform 0.3s;
}
.tl-node.active {
  opacity: 1;
  border-color: var(--accent);
  transform: scale(1.04);
  box-shadow: 0 0 0 2px var(--accent-dim);
}
.tl-arrow {
  color: var(--muted);
  font-size: 0.9rem;
  opacity: 0.5;
}
.motion-controls {
  margin-top: 0.85rem;
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
}

/* Buttons */
button, .btn {
  appearance: none;
  border: 1px solid var(--border);
  background: var(--surface-2);
  color: var(--text);
  font: inherit;
  font-size: 0.9rem;
  padding: 0.45rem 0.9rem;
  border-radius: 8px;
  cursor: pointer;
}
button:hover, .btn:hover {
  border-color: var(--accent);
  background: var(--accent-dim);
}
button:focus-visible, .btn:focus-visible, a:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}
button.primary {
  background: var(--accent-dim);
  border-color: var(--accent);
  font-weight: 600;
}
button:disabled {
  opacity: 0.45;
  cursor: not-allowed;
}

/* Topic cards (home) */
.topic-grid {
  display: grid;
  gap: 0.85rem;
}
.topic-card {
  display: block;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1rem 1.1rem;
  color: inherit;
  transition: border-color 0.15s, transform 0.15s;
}
.topic-card:hover {
  border-color: var(--accent);
  text-decoration: none;
  transform: translateY(-1px);
}
.topic-card .slug {
  font-size: 0.75rem;
  color: var(--muted);
  font-family: ui-monospace, monospace;
}
.topic-card .title {
  font-size: 1.1rem;
  font-weight: 650;
  margin: 0.25rem 0;
}
.topic-card .blurb {
  margin: 0;
  color: var(--muted);
  font-size: 0.9rem;
}

.lead {
  color: var(--muted);
  margin: 0 0 1.25rem;
  font-size: 0.95rem;
}

/* Quiz */
.quiz-q {
  margin-bottom: 1.25rem;
  padding-bottom: 1rem;
  border-bottom: 1px solid var(--border);
}
.quiz-q:last-of-type {
  border-bottom: none;
  margin-bottom: 0.5rem;
}
.quiz-q .q-label {
  font-weight: 650;
  margin: 0 0 0.55rem;
}
.quiz-options {
  display: flex;
  flex-direction: column;
  gap: 0.4rem;
}
.quiz-options label {
  display: flex;
  gap: 0.55rem;
  align-items: flex-start;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 0.55rem 0.7rem;
  cursor: pointer;
}
.quiz-options label:hover {
  border-color: var(--accent);
}
.quiz-options input {
  margin-top: 0.2rem;
  accent-color: var(--accent);
}
.quiz-feynman textarea {
  width: 100%;
  min-height: 4.5rem;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  color: var(--text);
  font: inherit;
  padding: 0.6rem;
  resize: vertical;
}
.quiz-feynman .hint {
  font-size: 0.8rem;
  color: var(--muted);
  margin: 0.35rem 0 0;
}

.feedback {
  margin-top: 0.55rem;
  padding: 0.5rem 0.7rem;
  border-radius: 8px;
  font-size: 0.9rem;
  display: none;
}
.feedback.show { display: block; }
.feedback.ok {
  background: color-mix(in srgb, var(--ok) 18%, transparent);
  border: 1px solid var(--ok);
  color: var(--ok);
}
.feedback.warn {
  background: color-mix(in srgb, var(--warn) 18%, transparent);
  border: 1px solid var(--warn);
  color: var(--warn);
}
.feedback.bad {
  background: color-mix(in srgb, var(--bad) 18%, transparent);
  border: 1px solid var(--bad);
  color: var(--bad);
}
.feedback a { color: inherit; text-decoration: underline; }

.quiz-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-top: 0.75rem;
}
.quiz-summary {
  margin-top: 1rem;
  padding: 0.75rem;
  background: var(--bg);
  border-radius: 8px;
  border: 1px solid var(--border);
  display: none;
}
.quiz-summary.show { display: block; }
.score-pill {
  display: inline-block;
  padding: 0.15rem 0.55rem;
  border-radius: 999px;
  font-size: 0.85rem;
  font-weight: 650;
}
.score-pill.ok { background: var(--ok); color: #0a1a10; }
.score-pill.warn { background: var(--warn); color: #1a1400; }
.score-pill.bad { background: var(--bad); color: #1a0505; }

/* Gap list */
.gap-list {
  margin: 0;
  padding-left: 1.2rem;
}
.gap-list li { margin-bottom: 0.4rem; }
.gap-list code {
  font-size: 0.85em;
  background: var(--bg);
  padding: 0.1rem 0.35rem;
  border-radius: 4px;
}

/* Next */
.next-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.75rem;
  align-items: center;
  justify-content: space-between;
}
.next-row p { margin: 0; color: var(--muted); font-size: 0.95rem; }

/* 404 */
.notfound {
  text-align: center;
  padding: 3rem 1rem;
}
.notfound h1 { font-size: 2rem; margin: 0 0 0.5rem; }
.notfound p { color: var(--muted); }

/* Sticky section jump (optional scannable TOC) */
.jump {
  display: flex;
  flex-wrap: wrap;
  gap: 0.4rem;
  margin-bottom: 1.25rem;
}
.jump a {
  font-size: 0.75rem;
  padding: 0.25rem 0.55rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 999px;
  color: var(--muted);
}
.jump a:hover {
  color: var(--accent);
  border-color: var(--accent);
  text-decoration: none;
}

@media (max-width: 480px) {
  :root { font-size: 17px; }
  .wrap { padding: 1rem 0.75rem 2.5rem; }
}