/* R25: long pages read one chapter at a time. */
.chapter-strip {
  display: block;
  margin: 28px 0 24px;
  padding: 16px 18px;
  border: 1px solid var(--line);
  border-radius: 16px;
  background: var(--surface);
  scroll-margin-top: calc(var(--reading-top, 0px) + var(--reading-bar, 0px) + 16px);
}
.chapter-head { display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 8px 16px; }
.chapter-where { margin: 0; font: 600 12px/1.4 ui-monospace, "SF Mono", Menlo, Consolas, monospace; letter-spacing: 0.08em; text-transform: uppercase; color: var(--accent); }
.chapter-mode { min-height: 36px; padding: 6px 14px; border: 1px solid var(--line); border-radius: 999px; background: transparent; color: var(--ink); font-size: 0.8125rem; font-weight: 600; }
.chapter-mode:hover { border-color: var(--accent); }
.chapter-list { list-style: none; margin: 12px 0 0; padding: 0; display: flex; flex-wrap: wrap; gap: 6px; }
.chapter-list li { margin: 0; }
.chapter-list a {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  min-height: 36px;
  max-width: 30ch;
  padding: 5px 12px 5px 6px;
  border: 1px solid var(--line);
  border-radius: 999px;
  color: var(--muted);
  font-size: 0.8125rem;
  line-height: 1.3;
  text-decoration: none;
}
.chapter-list a:hover { border-color: var(--accent); color: var(--ink); }
.chapter-n { flex: none; display: grid; place-items: center; width: 24px; height: 24px; border-radius: 50%; background: var(--soft); color: var(--ink); font: 600 var(--label-size)/1 ui-monospace, "SF Mono", Menlo, Consolas, monospace; }
.chapter-list a[aria-current] { border-color: var(--accent); color: var(--ink); background: var(--soft); }
.chapter-list a[aria-current] .chapter-n { background: var(--accent); color: var(--button-ink); }
.chapter-pager { display: none; }
/* fragile: Chromium 141 (Playwright 1.56.1) hidden="until-found": find-in-page and fragment links stop
   opening a closed chapter if Chromium stops supporting it. A page with chapters must exempt it
   from its own [hidden]{display:none} rule (see iommu-lab.css and iommu/validation.css). Closed
   chapters take no space: absolute, no margin, padding or border. */
@media screen {
  .chapter[hidden="until-found"] {
    position: absolute;
    inset-inline: 0;
    margin: 0;
    padding: 0;
    border: 0;
    background: transparent;
  }
}
main[data-chapter-mode="chapters"] .chapter-pager { display: flex; align-items: stretch; flex-wrap: wrap; justify-content: space-between; gap: 12px; margin-top: 36px; padding-top: 20px; border-top: 1px solid var(--line); }
.chapter-pager button {
  display: grid;
  gap: 4px;
  max-width: min(100%, 420px);
  min-height: 56px;
  padding: 12px 16px;
  border: 1px solid var(--line);
  border-radius: 14px;
  background: var(--bg);
  color: var(--ink);
  text-align: left;
  font-size: 0.9375rem;
  font-weight: 600;
  line-height: 1.35;
}
.chapter-pager .chapter-next { margin-left: auto; text-align: right; border-color: var(--accent); background: var(--soft); }
.chapter-pager button:hover { border-color: var(--accent); }
.chapter-pager .eyebrow { margin: 0; font-size: var(--label-size); color: var(--muted); }
main[data-chapter-mode="chapters"]:not([data-last-chapter]) + .reading-next { display: none; }
@media (max-width: 700px) {
  .chapter-list { flex-wrap: nowrap; overflow-x: auto; padding-bottom: 4px; scrollbar-width: thin; }
  .chapter-list li { flex: none; }  /* else the pills shrink to one letter per line */
  .chapter-list a { max-width: 24ch; }
  .chapter-pager button { max-width: 100%; flex: 1 1 100%; }
  .chapter-pager .chapter-next { text-align: left; }
}
@media print { .chapter-strip, .chapter-pager { display: none !important; } .chapter[hidden] { display: block !important; content-visibility: visible !important; } }
main[data-chapter-mode="chapters"] nav[aria-label="Playground sections"] { display: none; }