/**
 * lesson-articles-by-part.css — article picker grouped by Parts (cards + optional collapse on narrow screens).
 *
 * Markup (on <main> or any ancestor wrapping the nav):
 *   <main class="chapter-main stylish-chapter chapter-articles-by-part">
 *     <nav class="stylish-articles-list articles-by-part-nav" aria-label="…">
 *       <div class="articles-part" data-part="1">
 *         <div class="articles-part__header">… badge, intro, toggle …</div>
 *         <div class="articles-part__articles" id="…">… article buttons …</div>
 *       </div>
 *     </nav>
 *   </main>
 *
 * Pair with lesson-articles-by-part.js in $GLOBALS['COURSE_PAGE_SCRIPTS']. Accent colours use data-part="1" … "12".
 * Depends on article button / overlay styles from lesson-stylish-base.css (loaded on all lessons via header).
 */

.chapter-articles-by-part .visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.chapter-articles-by-part nav.stylish-articles-list.articles-by-part-nav {
  flex-direction: column;
  flex-wrap: nowrap;
  align-items: stretch;
  gap: 1.15rem;
  margin-bottom: 2.25rem;
}

.chapter-articles-by-part .articles-part {
  --part-accent: #0d9488;
  --part-accent-soft: rgba(13, 148, 136, 0.12);
  --part-border: rgba(15, 23, 42, 0.08);
  border: 1px solid var(--part-border, #e2e8f0);
  border-radius: 14px;
  background: linear-gradient(145deg, #fff 0%, #f8fafc 100%);
  box-shadow: 0 2px 10px rgba(15, 23, 42, 0.05);
  overflow: hidden;
}

.chapter-articles-by-part .articles-part[data-part="2"] {
  --part-accent: #1d4ed8;
  --part-accent-soft: rgba(29, 78, 216, 0.1);
}

.chapter-articles-by-part .articles-part[data-part="3"] {
  --part-accent: #7c3aed;
  --part-accent-soft: rgba(124, 58, 237, 0.1);
}

.chapter-articles-by-part .articles-part[data-part="4"] {
  --part-accent: #c2410c;
  --part-accent-soft: rgba(194, 65, 12, 0.1);
}

.chapter-articles-by-part .articles-part[data-part="5"] {
  --part-accent: #0f766e;
  --part-accent-soft: rgba(15, 118, 110, 0.12);
}

.chapter-articles-by-part .articles-part[data-part="6"] {
  --part-accent: #b45309;
  --part-accent-soft: rgba(180, 83, 9, 0.12);
}

.chapter-articles-by-part .articles-part[data-part="7"] {
  --part-accent: #4338ca;
  --part-accent-soft: rgba(67, 56, 202, 0.1);
}

.chapter-articles-by-part .articles-part[data-part="8"] {
  --part-accent: #be185d;
  --part-accent-soft: rgba(190, 24, 93, 0.1);
}

.chapter-articles-by-part .articles-part[data-part="9"] {
  --part-accent: #0e7490;
  --part-accent-soft: rgba(14, 116, 144, 0.12);
}

.chapter-articles-by-part .articles-part[data-part="10"] {
  --part-accent: #047857;
  --part-accent-soft: rgba(4, 120, 87, 0.1);
}

.chapter-articles-by-part .articles-part[data-part="11"] {
  --part-accent: #a21caf;
  --part-accent-soft: rgba(162, 28, 175, 0.1);
}

.chapter-articles-by-part .articles-part[data-part="12"] {
  --part-accent: #475569;
  --part-accent-soft: rgba(71, 85, 105, 0.12);
}

.chapter-articles-by-part .articles-part__header {
  display: grid;
  grid-template-columns: auto 1fr auto;
  align-items: start;
  gap: 0.85rem 1rem;
  padding: 1rem 1.1rem 0.85rem;
  border-bottom: 1px solid var(--part-border, #e2e8f0);
  background: linear-gradient(90deg, var(--part-accent-soft), transparent 55%);
}

.chapter-articles-by-part .articles-part__badge {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 2.35rem;
  height: 2.35rem;
  padding: 0 0.45rem;
  border-radius: 10px;
  font-size: 0.95rem;
  font-weight: 800;
  letter-spacing: 0.02em;
  color: #fff;
  background: var(--part-accent, #0d9488);
  box-shadow: 0 2px 6px rgba(15, 23, 42, 0.12);
}

.chapter-articles-by-part .articles-part__intro {
  min-width: 0;
}

.chapter-articles-by-part .articles-part__title {
  margin: 0 0 0.35rem;
  font-size: 1.05rem;
  font-weight: 700;
  line-height: 1.35;
  color: var(--text, #0f172a);
}

.chapter-articles-by-part .articles-part__summary {
  margin: 0 0 0.45rem;
  font-size: 0.9rem;
  line-height: 1.5;
  color: #475569;
}

.chapter-articles-by-part .articles-part__range {
  margin: 0;
  font-size: 0.8rem;
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: #64748b;
  font-weight: 600;
}

.chapter-articles-by-part .articles-part__range strong {
  color: var(--part-accent, #0d9488);
  font-weight: 800;
}

.chapter-articles-by-part .articles-part__toggle {
  display: none;
  align-self: center;
  width: 2.5rem;
  height: 2.5rem;
  padding: 0;
  border: 1px solid var(--border, #e2e8f0);
  border-radius: 10px;
  background: #fff;
  cursor: pointer;
  color: var(--text, #0f172a);
  transition: background 0.15s, border-color 0.15s, transform 0.2s;
}

.chapter-articles-by-part .articles-part__toggle:hover {
  border-color: var(--part-accent, #0d9488);
  background: var(--part-accent-soft);
}

.chapter-articles-by-part .articles-part__toggle:focus-visible {
  outline: 2px solid var(--part-accent, #0d9488);
  outline-offset: 2px;
}

.chapter-articles-by-part .articles-part__toggle-icon {
  display: block;
  width: 100%;
  height: 100%;
  position: relative;
}

.chapter-articles-by-part .articles-part__toggle-icon::before {
  content: "";
  position: absolute;
  left: 50%;
  top: 50%;
  width: 0.55rem;
  height: 0.55rem;
  margin: -0.2rem 0 0 -0.2rem;
  border-right: 2px solid currentColor;
  border-bottom: 2px solid currentColor;
  transform: rotate(45deg);
  transition: transform 0.2s ease;
}

.chapter-articles-by-part .articles-part.is-collapsed .articles-part__toggle-icon::before {
  transform: rotate(-135deg);
  margin-top: -0.05rem;
}

.chapter-articles-by-part .articles-part__articles {
  display: flex;
  flex-wrap: wrap;
  gap: 0.65rem;
  padding: 0.85rem 1rem 1.05rem;
}

.chapter-articles-by-part .articles-part.is-collapsed .articles-part__articles {
  display: none;
}

@media (max-width: 52rem) {
  .chapter-articles-by-part .articles-part__toggle {
    display: inline-flex;
    align-items: center;
    justify-content: center;
  }
}