/**
 * ============================================================================
 * collapsible.css - Collapsible section (button + panel, slide animation)
 * ============================================================================
 *
 * Used below the calculator: one visible intro block, then expandable sections.
 * Content remains in the DOM for SEO. JS toggles .collapsible--open for
 * accessibility (aria-expanded) and so we can animate both open and close.
 *
 * ANIMATION:
 *   Same system as slide-up sheet: --ease-out, --animate-duration-panel
 *   (tokens.css). Content slides down/up via grid-template-rows 0fr ↔ 1fr.
 *   prefers-reduced-motion: base.css shortens all transitions site-wide.
 *
 * ============================================================================
 */

.collapsible {
  margin-top: var(--space-md);
  border: 1.5px solid var(--color-border);
  border-radius: var(--radius-md);
  overflow: hidden;
  transition: border-color var(--transition-fast);
}

.collapsible__summary {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-sm);
  width: 100%;
  padding: var(--space-md) var(--space-lg);
  font-weight: var(--weight-medium);
  font-size: inherit;
  font-family: inherit;
  text-align: left;
  cursor: pointer;
  border: none;
  background-color: transparent;
  color: inherit;
  transition: background-color var(--transition-fast);
}

.collapsible__summary:hover {
  background-color: var(--color-surface);
}

.collapsible__summary:focus-visible {
  outline: 2px solid var(--color-accent);
  outline-offset: 2px;
}

.collapsible__title {
  flex: 1;
}

.collapsible__icon {
  flex-shrink: 0;
  transition: transform var(--animate-duration-panel) var(--ease-out);
  color: var(--color-text-muted);
}

.collapsible--open .collapsible__icon {
  transform: rotate(180deg);
}

/* --- Content: slide down/up via grid (same easing as sheet) --- */
.collapsible__content {
  display: grid;
  grid-template-rows: 0fr;
  transition: grid-template-rows var(--animate-duration-panel) var(--ease-out);
}

.collapsible--open .collapsible__content {
  grid-template-rows: 1fr;
}

/* Inner has no padding/border so the 0fr grid row clips fully (no peeking) */
.collapsible__content-inner {
  min-height: 0;
  overflow: hidden;
}

.collapsible__content-body {
  padding: var(--space-md) var(--space-lg);
  border-top: 1px solid var(--color-border);
}

.collapsible__content-body > *:first-child {
  margin-top: 0;
}

.collapsible__content-body > *:last-child {
  margin-bottom: 0;
}

.collapsible__content-body h3 {
  margin-top: var(--space-lg);
  font-size: var(--text-base);
}

.collapsible__content-body h3:first-child {
  margin-top: 0;
}

.collapsible__content-body p,
.collapsible__content-body ul {
  margin-top: var(--space-sm);
}