/* Scoped navigation for study pages. The homepage and study mode controls are unchanged. */
.pd-mobile-navigation, .pd-mobile-topic-jump, .pd-mobile-topic-trail, .pd-mobile-alltopics { display: none; }

@media (max-width: 900px) {
  .pd-mobile-navigation { display: flex; flex-wrap: wrap; align-items: start; gap: 8px; min-width: 0; }
  .pd-mobile-collections { display: flex; flex: 1 1 auto; flex-wrap: nowrap; align-items: stretch; gap: 8px; margin: 0; }
  .pd-mobile-collections a, .pd-mobile-subjects > summary, .pd-mobile-topic-jump > summary {
    box-sizing: border-box; display: flex; align-items: center; justify-content: center; min-height: 44px;
    margin: 0; padding: 8px 12px; border: 1px solid var(--pd-line); border-radius: 10px;
    background: var(--pd-surface); color: var(--pd-text); font-size: 13px; font-weight: 600; text-decoration: none;
  }
  .pd-mobile-collections a { flex: 1 1 auto; }
  .pd-mobile-subjects { flex: 0 0 auto; min-width: 0; padding: 0; margin: 0; border: 0; background: none; }
  .pd-mobile-subjects[open] { flex-basis: 100%; }
  .pd-mobile-subjects > summary, .pd-mobile-topic-jump > summary { cursor: pointer; list-style: none; justify-content: space-between; gap: 12px; }
  .pd-mobile-subjects > summary::after, .pd-mobile-topic-jump > summary::after { content: '+'; font-size: 18px; line-height: 1; }
  .pd-mobile-subjects[open] > summary::after, .pd-mobile-topic-jump[open] > summary::after { content: '−'; }
  .pd-mobile-subjects > summary::-webkit-details-marker, .pd-mobile-topic-jump > summary::-webkit-details-marker { display: none; }
  .pd-mobile-subject-list, .pd-mobile-topic-list { display: grid; gap: 4px; padding: 10px 0 2px; }
  .pd-mobile-group { margin: 10px 0 4px; color: var(--pd-muted); font-size: 12px; font-weight: 650; }
  .pd-mobile-group:first-child { margin-top: 0; }
  .pd-mobile-subject, .pd-mobile-topic-list a {
    display: flex; align-items: center; box-sizing: border-box; min-height: 44px; padding: 10px 12px; width: 100%;
    margin: 0; border: 1px solid var(--pd-line); border-radius: 8px; color: var(--pd-text); background: var(--pd-surface);
    font: 500 14px/1.4 var(--pd-font-text); text-align: left; text-decoration: none; overflow-wrap: anywhere;
  }
  .pd-mobile-subject[aria-current] { border-color: var(--pd-cobalt); font-weight: 650; }
  .pd-mobile-subject:hover, .pd-mobile-topic-list a:hover, .pd-mobile-collections a:hover { background: var(--pd-surface-2); }
  .pd-mobile-navigation a:focus-visible, .pd-mobile-navigation button:focus-visible,
  .pd-mobile-navigation summary:focus-visible, .pd-mobile-topic-jump summary:focus-visible,
  .pd-mobile-topic-list a:focus-visible { outline: 3px solid var(--pd-cobalt); outline-offset: 2px; }
  .pd-mobile-topic-trail { display: flex; flex-wrap: wrap; justify-content: flex-start; gap: 4px 8px; margin: 8px 0 12px; font-size: 13px; }
  .pd-mobile-topic-trail a { display: inline-flex; align-items: center; min-height: 36px; overflow-wrap: anywhere; }
  .pd-mobile-topic-trail span { align-self: center; color: var(--pd-muted); }
  .pd-mobile-topic-jump { display: block; margin: 14px 0; padding: 0; border: 0; background: none; }
  .pd-fc-main #library, .pd-fc-main #rotations { scroll-margin-top: 82px; }
  .study-nav .pd-mobile-navigation { display: none; margin: 0 0 12px; }
}

@media (max-width: 700px) {
  /* Publisher links can exceed the phone header; keep them scrollable within it. */
  .topbar { overflow-x: auto; overscroll-behavior-x: contain; }
  .study-nav .pd-mobile-navigation { display: flex; }
  .pd-mobile-alltopics { display: block; margin: 10px 0; min-height: 36px; line-height: 36px; }
  /* Wrap topic names in a short vertical list instead of an off-screen horizontal strip. */
  .study-page .study-nav-buttons { display: block; overflow: visible; }
  .study-page .study-nav-buttons > .topic-btn, .study-page .topic-btn.topic-child {
    display: flex; align-items: center; justify-content: space-between; gap: 10px; min-height: 44px;
    width: 100%; margin: 0 0 6px; padding: 10px 12px; white-space: normal; overflow-wrap: anywhere;
  }
  .study-page .topic-sub { display: block; }
  .study-page .study-nav-buttons .topic-n { flex: 0 0 auto; }
  /* Phone users navigate with the labelled topic buttons and subject switcher. */
  .study-page .study-nav-select { display: none; }
  .study-mbar-btn { min-height: 44px; }
}