nav.toc {
  background: #f8f8f8;
  border-left: 3px solid #ccc;
  margin-bottom: 2rem;
  border-radius: 2px;
}

nav.toc details {
  padding: 12px 20px;
}

nav.toc summary {
  cursor: pointer;
  font-size: 16px;
  font-weight: bold;
  text-transform: uppercase;
  letter-spacing: 0.05em;
  color: #666;
  user-select: none;
  list-style: none;
}

nav.toc summary::-webkit-details-marker {
  display: none;
}

nav.toc summary::before {
  content: "▶ ";
  font-size: 11px;
  vertical-align: middle;
}

nav.toc details[open] summary::before {
  content: "▼ ";
}

nav.toc ul {
  margin: 12px 0 0 0;
  padding-left: 20px;
  font-size: 17px;
}

nav.toc li {
  margin: 5px 0;
  line-height: 1.5;
}

nav.toc a {
  color: #555;
  text-decoration: none;
}

nav.toc a:hover {
  color: #000;
  text-decoration: underline;
}