.book {
  display: flex;
  align-items: flex-start;
  gap: clamp(20px, 3.5vw, 52px);
  max-width: 1120px;
  margin: 0 auto;
  padding: 0 20px;
}

.book main {
  flex: 1;
  min-width: 0;
  max-width: 720px;
  margin: 0;
  padding-left: 0;
  padding-right: 0;
}

.book .toc {
  flex: none;
  width: 214px;
  position: sticky;
  top: 24px;
  padding-top: clamp(40px, 7vw, 76px);
  font-size: 13.5px;
  line-height: 1.65;
  max-height: calc(100vh - 48px);
  overflow-y: auto;
  overscroll-behavior: contain;
}

.book .toc-h {
  font-family: 'IBM Plex Mono', monospace;
  font-size: 11px;
  letter-spacing: .12em;
  color: var(--dim);
  margin-bottom: 10px;
  padding-left: 10px;
}

.book .toc ol { list-style: none; margin: 0; padding: 0; font-size: inherit; }

.book .toc a {
  display: block;
  color: var(--dim2);
  text-decoration: none;
  padding: 5px 10px;
  border-radius: 7px;
}
.book .toc a:hover { color: var(--ink); background: var(--card); }

.book .toc .page > a { color: var(--ink); font-weight: 700; background: none; }
.book .toc .page > a:hover { background: var(--card); }

.book .toc .chs {
  margin: 2px 0 8px 10px;
  padding-left: 10px;
  border-left: 1px solid var(--border);
}
.book .toc .chs a { font-size: 13px; padding: 4px 8px; }
.book .toc .chs a.on { color: var(--ink); background: var(--card); font-weight: 600; }

.book .toc.gnav { display: block; justify-content: initial; border-bottom: 0; padding-bottom: 0; }

.book main h2 { scroll-margin-top: 20px; }

@media (max-width: 900px) {
  .book { display: block; padding: 0; max-width: none; }
  .book main { max-width: 720px; margin: 0 auto; padding-left: 20px; padding-right: 20px; }
  .book .toc {
    position: static; width: auto; max-height: none; overflow: visible;
    padding: 12px 20px; border-bottom: 1px solid var(--border);
  }
  .book .toc-h, .book .toc .chs { display: none; }
  .book .toc ol { display: flex; flex-wrap: wrap; gap: 4px; justify-content: center; }
  .book .toc a { padding: 5px 12px; border-radius: 999px; white-space: nowrap; }
}