.chapter-nav {
  position: fixed;
  z-index: 30;
  top: 16px;
  bottom: 16px;
  left: max(16px, calc((100vw - 1400px) / 2));
  width: 286px;
  overflow-y: auto;
  padding: 14px;
  border: 1px solid var(--line);
  border-radius: 12px;
  background: var(--surface);
  box-shadow: var(--shadow);
}
.chapter-nav-toggle { display: flex; width: 100%; align-items: center; gap: 8px; padding: 0 0 10px; border: 0; border-bottom: 1px solid var(--line); background: transparent; color: var(--muted); font: inherit; font-size: 12px; cursor: pointer; }
.chapter-nav-toggle:hover { color: var(--accent); }
.chapter-nav-content { padding-top: 12px; }
.chapter-nav-heading { display: flex; justify-content: space-between; gap: 12px; margin-bottom: 14px; }
.chapter-nav-heading strong { min-width: 0; color: var(--ink); font-size: 14px; font-weight: 500; line-height: 1.4; }
.chapter-nav-heading span { flex: 0 0 auto; color: var(--muted); font-size: 12px; }
.chapter-nav-list { display: grid; gap: 2px; }
.chapter-nav-module { margin: 0 0 16px; }
.chapter-nav-module h2 { margin: 0 0 5px; color: var(--muted-strong); font: 500 12px/1.4 var(--font-sans); }
.chapter-nav-list a { display: grid; gap: 2px; padding: 7px 8px; border-radius: 6px; color: var(--muted); text-decoration: none; }
.chapter-nav-list a:hover { color: var(--ink); background: var(--surface-raised); }
.chapter-nav-list a.is-current { color: var(--accent); background: color-mix(in srgb, var(--accent) 18%, var(--surface-raised)); }
.chapter-nav-code { color: var(--accent); font-size: 11px; }
.chapter-nav-title { font-size: 13px; line-height: 1.4; }
body:has(.chapter-nav) .course-shell, body:has(.chapter-nav) .site-shell, body:has(.chapter-nav) .app, body:has(.chapter-nav) .page { max-width: 1400px; padding-left: 326px; }
.chapter-nav.is-collapsed { width: 48px; overflow: hidden; padding-inline: 10px; }
.chapter-nav.is-collapsed .chapter-nav-content, .chapter-nav.is-collapsed .chapter-nav-toggle-label { display: none; }
.chapter-nav.is-collapsed .chapter-nav-toggle { justify-content: center; border-bottom: 0; }
.chapter-nav.is-collapsed .chapter-nav-toggle span[aria-hidden="true"] { transform: rotate(180deg); }
body:has(.chapter-nav.is-collapsed) .course-shell, body:has(.chapter-nav.is-collapsed) .site-shell, body:has(.chapter-nav.is-collapsed) .app, body:has(.chapter-nav.is-collapsed) .page { padding-left: 88px; }
@media (max-width: 1240px) {
  .chapter-nav { width: 48px; overflow: hidden; padding-inline: 10px; }
  .chapter-nav .chapter-nav-content, .chapter-nav .chapter-nav-toggle-label { display: none; }
  .chapter-nav .chapter-nav-toggle { justify-content: center; border-bottom: 0; }
  .chapter-nav .chapter-nav-toggle span[aria-hidden="true"] { transform: rotate(180deg); }
  .chapter-nav.is-expanded { width: min(300px, calc(100vw - 24px)); padding-inline: 14px; }
  .chapter-nav.is-expanded .chapter-nav-content { display: block; }
  .chapter-nav.is-expanded .chapter-nav-toggle-label { display: inline; }
  .chapter-nav.is-expanded .chapter-nav-toggle { justify-content: flex-start; border-bottom: 1px solid var(--line); }
  .chapter-nav.is-expanded .chapter-nav-toggle span[aria-hidden="true"] { transform: none; }
  body:has(.chapter-nav) .course-shell, body:has(.chapter-nav) .site-shell, body:has(.chapter-nav) .app, body:has(.chapter-nav) .page, body:has(.chapter-nav.is-collapsed) .course-shell, body:has(.chapter-nav.is-collapsed) .site-shell, body:has(.chapter-nav.is-collapsed) .app, body:has(.chapter-nav.is-collapsed) .page { padding-left: 84px; }
}
@media (max-width: 760px) { .chapter-nav { display: none; } body:has(.chapter-nav) .course-shell, body:has(.chapter-nav) .site-shell, body:has(.chapter-nav) .app, body:has(.chapter-nav) .page { padding-left: 20px; } }