MediaWiki:CollapsibleTree.css

/* Hide nested lists by default to prevent FOUC */
.collapsible-tree > ul ul {
  display: none;
}

.collapsible-tree > ul {
  margin: 0;
  padding-left: 28px;
  list-style: none;
  line-height: 2.2em;
}

.collapsible-tree > ul li {
  position: relative;
  transition: all 0.2s ease;
}

.collapsible-tree > ul li a {
  padding-left: 0.5rem;
  color: #2563eb;
  text-decoration: none;
  transition: color 0.2s ease;
}

.collapsible-tree > ul li a:hover {
  color: #1e40af;
  text-decoration: underline;
}

/* Modern tree lines with smoother styling */
.collapsible-tree > ul li::before,
.collapsible-tree > ul li::after {
  content: "";
  position: absolute;
  left: -18px;
  border-left: 1px solid #d1d5db;
}

.collapsible-tree > ul li::before {
  top: 0;
  width: 18px;
  height: 1.1em;
  border-bottom: 1px solid #d1d5db;
}

/* Hide vertical line for first item */
.collapsible-tree > ul > li:first-child::before {
  border-left: none;
}

.collapsible-tree > ul li::after {
  top: 1.1em;
  bottom: 1px;
}

/* Hide lines for last item */
.collapsible-tree > ul li:last-child::after {
  display: none;
}

/* Modern toggle icon */
.js-toggle-icon {
  position: relative;
  z-index: 1;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 18px;
  height: 18px;
  margin: 0 4px 0 -26px;
  cursor: pointer;
  font-style: normal;
  font-size: 12px;
  font-weight: 600;
  background: linear-gradient(135deg, #f9fafb 0%, #f3f4f6 100%);
  border: 1px solid #d1d5db;
  border-radius: 3px;
  color: #4b5563;
  transition: all 0.2s ease;
  user-select: none;
  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.05);
}

.js-toggle-icon:hover {
  background: linear-gradient(135deg, #ffffff 0%, #f9fafb 100%);
  border-color: #9ca3af;
  color: #1f2937;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
  transform: scale(1.05);
}

.js-toggle-icon:active {
  transform: scale(0.95);
  box-shadow: 0 0 0 rgba(0, 0, 0, 0.05);
}

/* Highlight parent items with children */
.collapsible-tree > ul li.has-children > a {
  font-weight: 500;
}

/* Optional: Add subtle hover effect to tree items */
.collapsible-tree > ul li:hover > a {
  background-color: rgba(59, 130, 246, 0.05);
  border-radius: 3px;
  margin-left: -4px;
  padding-left: calc(0.5rem + 4px);
}