llvm/clang-tools-extra/docs/_static/clang-tools-extra-styles.css

details {
  background-color: rgba(50, 150, 220, 0.08);
  margin-bottom: 0.5em;
  padding: 0 1em;
  overflow-y: hidden; /* Suppress margin-collapsing */
}
details[open] {
  border-bottom: 1px solid rgba(0, 0, 128, 0.2);
  margin-bottom: 1em;
}
details summary {
  font-weight: bold;
  background-color: rgba(50, 150, 220, 0.1);
  border-color: rgba(0, 0, 128, 0.2);
  border-width: 1px;
  border-style: solid none;
  padding: 0.2em;
  margin: 0 -1em;
}
details summary:hover {
  background-color: rgba(50, 150, 220, 0.2);
  cursor: pointer;
}