@layer components {
  .collapsible {
    border: 1px solid var(--border);
    border-radius: var(--radius-lg);
    overflow: hidden;

    /* Two gotchas, both required for the panel to glide:
       1. `::details-content` must attach to the compound (`&::details-content`,
          NOT `& ::details-content` — the descendant form never matches, the
          pseudo's originating element is the subject itself).
       2. `block-size: auto` is a keyword — without interpolate-size the
          0→auto pair is non-interpolable and the transition silently snaps. */
    &::details-content {
      block-size: 0;
      overflow-y: clip;
      interpolate-size: allow-keywords;
      transition: block-size 200ms ease, content-visibility 200ms allow-discrete;
    }

    &[open]::details-content {
      block-size: auto;
    }
  }

  @starting-style {
    .collapsible[open]::details-content {
      block-size: 0;
    }
  }

  .collapsible-trigger {
    display: flex;
    align-items: center;
    justify-content: space-between;
    width: 100%;
    padding: 0.75rem 1rem;
    font-size: 0.875rem;
    font-weight: 500;
    cursor: pointer;
    color: var(--foreground);
    list-style: none;

    &:hover {
      background-color: var(--accent);
    }

    &:focus-visible {
      outline: 2px solid var(--ring);
      outline-offset: -2px;
    }

    &::-webkit-details-marker {
      display: none;
    }
  }

  .collapsible-chevron {
    width: 1rem;
    height: 1rem;
    color: var(--muted-foreground);
    transition: transform 200ms ease;
    flex-shrink: 0;

    details[open] > summary > & {
      transform: rotate(180deg);
    }
  }

  .collapsible-content {
    padding: 0 1rem 0.75rem;
    font-size: 0.875rem;
    color: var(--muted-foreground);
    line-height: 1.6;
  }
}

/* Accessibility: suppress motion for users who request it (REQUIRED for all
   components — AGENTS.md "Accessibility CSS"). Near-zero duration instead of
   `none` keeps transitionend/animationend (and discrete display flips)
   firing so JS state machines that await them keep working. */
@media (prefers-reduced-motion: reduce) {
  @layer components {
    .collapsible,
    .collapsible *,
    .collapsible::before,
    .collapsible::after,
    .collapsible *::before,
    .collapsible *::after,
    .collapsible::backdrop,
    .collapsible::details-content,
    .collapsible-chevron,
    .collapsible-chevron *,
    .collapsible-chevron::before,
    .collapsible-chevron::after,
    .collapsible-chevron *::before,
    .collapsible-chevron *::after,
    .collapsible-chevron::backdrop,
    .collapsible-content,
    .collapsible-content *,
    .collapsible-content::before,
    .collapsible-content::after,
    .collapsible-content *::before,
    .collapsible-content *::after,
    .collapsible-content::backdrop,
    .collapsible-trigger,
    .collapsible-trigger *,
    .collapsible-trigger::before,
    .collapsible-trigger::after,
    .collapsible-trigger *::before,
    .collapsible-trigger *::after,
    .collapsible-trigger::backdrop {
      transition-duration: 0.01ms !important;
      animation-duration: 0.01ms !important;
      animation-iteration-count: 1 !important;
    }
  }
}