:root {
  --bg: #ffffff;
  --fg: #141414;
  --muted: #6b7280;
  --card: #f7f7f8;
  --border: #e5e7eb;
  --accent: #0f62fe;
  --focus: 2px solid #0f62fe;
  --radius: 12px;
  --shadow: 0 6px 30px rgba(0,0,0,0.08);
}
:root.dark {
  --bg: #0b0b0c;
  --fg: #e6e7ea;
  --muted: #9aa0aa;
  --card: #141416;
  --border: #24262a;
  --accent: #78a6ff;
  --shadow: 0 8px 32px rgba(0,0,0,0.35);
}
* { box-sizing: border-box; }
html,body { height: 100%; scroll-behavior: smooth; }
body {
  margin: 0; background: var(--bg); color: var(--fg);
  font: 16px/1.65 "Noto Sans", system-ui, -apple-system, Segoe UI, Roboto, Arial, sans-serif;
  text-rendering: optimizeLegibility; -webkit-font-smoothing: antialiased;
}
.container { max-width: 1100px; margin: 0 auto; padding: 0 20px; }
.skip-link { position: absolute; left: -999px; top: -999px; }
.skip-link:focus { left: 16px; top: 16px; background: var(--bg); color: var(--fg); padding: 8px 12px; border: 1px solid var(--border); border-radius: 6px; }

.site-header { position: sticky; top: 0; z-index: 50; background: var(--bg); border-bottom: 1px solid var(--border); backdrop-filter: saturate(1.2) blur(6px); }
.header-inner { display: grid; grid-template-columns: auto 1fr auto; gap: 16px; align-items: center; padding: 14px 0; }
.brand { display: flex; gap: 10px; align-items: center; font-weight: 700; letter-spacing: .2px; }
.brand-mark { font-family: "Space Mono", monospace; }
.brand-text { white-space: nowrap; }
.site-nav .nav-toggle { display: none; }
.nav-list { display: flex; gap: 14px; list-style: none; padding: 0; margin: 0; }
.nav-list a { color: var(--fg); text-decoration: none; padding: 8px 10px; border-radius: 8px; }
.nav-list a:hover, .nav-list a.is-active { background: var(--card); }
.actions { display: flex; gap: 10px; align-items: center; }
.search { position: relative; display: inline-flex; align-items: center; }
.search input {
  width: 220px; padding: 8px 28px 8px 12px; border: 1px solid var(--border);
  border-radius: 999px; background: var(--bg); color: var(--fg);
}
.search .kbd { position: absolute; right: 8px; font: 12px/1 "Space Mono", monospace; color: var(--muted); }
.theme-toggle { border: 1px solid var(--border); background: var(--bg); color: var(--fg); border-radius: 999px; padding: 8px 10px; cursor: pointer; }

.hero { padding: 56px 0 24px; border-bottom: 1px solid var(--border); }
.hero h1 { font-size: 40px; line-height: 1.15; margin: 0 0 10px; letter-spacing: -0.5px; }
.subtitle { color: var(--muted); max-width: 60ch; }
.cta-row { display: flex; gap: 10px; margin-top: 18px; }
.btn { border: 1px solid var(--border); padding: 10px 14px; border-radius: 10px; text-decoration: none; color: var(--fg); transition: transform .15s ease, background .15s ease; }
.btn:hover { transform: translateY(-1px); background: var(--card); }
.btn.primary { background: var(--fg); color: var(--bg); border-color: var(--fg); }
.btn.primary:hover { transform: translateY(-1px); filter: brightness(1.05); }

.layout { display: grid; grid-template-columns: 260px 1fr; gap: 24px; padding: 28px 0 60px; }
.toc { position: sticky; top: 76px; align-self: start; }
.toc-title { margin: 8px 0 10px; font-size: 14px; color: var(--muted); }
.toc-list { list-style: none; padding: 0; margin: 0 0 12px; display: grid; gap: 6px; }
.toc-list a { text-decoration: none; color: var(--fg); padding: 6px 8px; border-radius: 8px; }
.toc-list a:hover, .toc-list a.is-active { background: var(--card); }
.search-results { border: 1px dashed var(--border); border-radius: 10px; padding: 8px; font-size: 14px; color: var(--muted); display: none; }

.card {
  background: var(--card); border: 1px solid var(--border);
  border-radius: var(--radius); padding: 18px 18px 10px; box-shadow: var(--shadow);
}
.card + .card { margin-top: 18px; }

.collapsible-header { display: flex; justify-content: space-between; align-items: center; gap: 10px; }
.collapse-btn { border: 1px solid var(--border); background: transparent; color: var(--fg); padding: 6px 10px; border-radius: 8px; cursor: pointer; }
.collapsible-body { margin-top: 8px; }
details { background: var(--bg); border: 1px solid var(--border); border-radius: 10px; padding: 10px 12px; margin: 8px 0; }

.grid.two { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.bulleted { padding-left: 18px; }
.note { color: var(--muted); }
.checklist { list-style: none; padding: 0; }
.checklist li { display: flex; align-items: center; gap: 10px; padding: 6px 0; }

.quiz { display: grid; gap: 12px; }
.quiz .q { padding: 12px; background: var(--bg); border: 1px solid var(--border); border-radius: 10px; }
.quiz .q h4 { margin: 0 0 8px; }
.quiz-result { margin-top: 12px; font-weight: 600; }

.site-footer { border-top: 1px solid var(--border); padding: 18px 0 40px; color: var(--muted); }
.small { font-size: 13px; color: var(--muted); }

@media (max-width: 960px) {
  .layout { grid-template-columns: 1fr; }
  .toc { position: static; order: -1; }
}
@media (max-width: 720px) {
  .nav-list { display: none; position: absolute; top: 56px; right: 20px; background: var(--bg); border: 1px solid var(--border); border-radius: 12px; padding: 10px; box-shadow: var(--shadow); }
  .site-nav .nav-toggle { display: inline-block; border: 1px solid var(--border); background: var(--bg); border-radius: 8px; padding: 8px 10px; }
  .nav-list.show { display: grid; gap: 6px; }
  .hero h1 { font-size: 32px; }
  .grid.two { grid-template-columns: 1fr; }
  .search input { width: 150px; }
}

@media (prefers-reduced-motion: no-preference) {
  .card, .btn { transition: transform .2s ease, background .2s ease, box-shadow .2s ease; }
  a:hover { transition: background .15s ease; }
}

:focus-visible { outline: var(--focus); outline-offset: 2px; border-radius: 6px; }