.topic-card {
  background: var(--background);
  border-radius: 12px;
  padding: 15px 20px;
  margin-bottom: 20px;
  box-shadow: 0 4px 8px var(--shadow);
  cursor: pointer;
  transition: background 0.3s ease;
}

.topic-card.open .subtopics-list {
  max-height: 1000px;
  opacity: 1;
  margin-top: 15px;
}

.topic-card.open .subtopics-list a {
  text-decoration: none;
}

.topic-card .subtopics-list {
  max-height: 0;
  overflow: hidden;
  opacity: 0;
  transition: all 0.3s ease;
}

.topic-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.topic-card h3 {
  margin: 0;
  font-size: 1.1em;
}

.topic-card .arrow {
  font-size: 1.2em;
  transform: rotate(0deg);
  transition: transform 0.3s ease;
}

.topic-card.open .arrow {
  transform: rotate(180deg);
}

.subtopic-item {
  background-color: var(--background);
  border-left: 4px solid var(--primary);
  padding: 12px 16px;
  margin-top: 10px;
  border-radius: 8px;
  box-shadow: 0 1px 4px var(--shadow);
}

.subtopic-item:hover {
  background-color: var(--primary-hover);
  cursor: pointer;
  border-color: #38bdf8;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.08);
}

html.mode-dark .subtopic-item:hover {
  background-color: #38bdf8;
  color: var(--white);
}

.subtopic-item a {
  font-size: 1.05em;
  font-weight: 600;
  color: var(--primary);
  text-decoration: none;
}

.subtopic-item a:hover {
  text-decoration: underline;
}

.subtopic-item .description {
  color: var(--accent);
  font-size: 0.9em;
  margin-top: 5px;
}

html.mode-dark .subtopic-item .description {
  color: #aaa;
}

.subtopic-item .teacher {
  font-size: 0.85em;
  margin-top: 4px;
  color: #666;
}

html.mode-dark .subtopic-item .teacher {
  color: #ccc;
}