body {
  padding: 2rem;
  color: #343a40;
  font-size: large;
}

h1 {
  font-size: 1.8rem;
  margin-bottom: 1rem;
}

ul.tree, ul.tree ul {
  list-style-type: none;
  padding-left: 1rem;
}

ul.tree li {
  margin: 0.5rem 0;
}

.folder {
  cursor: pointer;
  font-weight: bold;
  display: inline-block;
}

.folder::before {
  content: "--";
  display: inline-block;
  margin-right: 0.4rem;
  transform: rotate(0deg);
  transition: transform 0.2s;
}

.folder.open::before {
  transform: rotate(90deg);
}

.nested {
  display: none;
  margin-left: 1.5rem;
}

.nested.active {
  display: block;
}

a {
  text-decoration: none;
  color: #0066cc;
}

a:hover {
  text-decoration: underline;
}