/**
 * Ambient TOC list: chapter modules (top-level nav list) fade; sidebar chrome/background stays solid.
 * Only on book *reading* pages (.reader-sidebar--ambient-toc); hub pages stay full-opacity TOC.
 * Touch devices (no hover): unchanged — TOC stays fully visible.
 */

@media (hover: hover) and (min-width: 768px) {
  .reader-sidebar.reader-sidebar--ambient-toc[data-reader-region="sidebar"] .reader-sidebar-slot nav > ul {
    opacity: 0.2;
    transition: opacity 0.9s ease;
  }

  /* Assignment links: avoid initial opacity transition shimmer on first reveal. */
  .assignment-focus .reader-sidebar.reader-sidebar--ambient-toc[data-reader-region="sidebar"] .reader-sidebar-slot nav > ul {
    transition: none;
  }

  /* Hover: pointer on sidebar. Keyboard: :focus-visible only (avoids stuck opacity after clicking <summary>). */
  .reader-sidebar.reader-sidebar--ambient-toc[data-reader-region="sidebar"]:hover .reader-sidebar-slot nav > ul,
  .reader-sidebar.reader-sidebar--ambient-toc[data-reader-region="sidebar"]:focus-within:has(:focus-visible) .reader-sidebar-slot nav > ul {
    opacity: 1;
    transition: opacity 0.18s ease;
  }
}

@media (prefers-reduced-motion: reduce) {
  @media (hover: hover) and (min-width: 768px) {
    .reader-sidebar.reader-sidebar--ambient-toc[data-reader-region="sidebar"] .reader-sidebar-slot nav > ul {
      transition: none;
      opacity: 1;
    }
  }
}