.folder {
  margin-bottom: 1em;
}
button {
  display: block;
  width: 100%;
  text-align: left;
  font-weight: bold;
  background: #eee;
  border: 1px solid #ccc;
  padding: 0.5em;
  cursor: pointer;
  font-size: 1rem;
  border-radius: 4px;
}
.folder-header:hover {
  background: #ddd;
}
ul {
  list-style-type: none;
  padding-left: 1em;
  margin-top: 0.5em;
}
li a {
  text-decoration: none;
  color: #0077cc;
}
li a:hover {
  text-decoration: underline;
}