mylloon.fr/static/css/cours.css

/* Filetree */
aside {
  float: left;
  margin-left: 20px;
}

aside ul {
  list-style: none;
  padding-left: 0.6em;
}

aside li {
  position: relative;
}

/* Element */
aside li:before {
  content: "";
  position: absolute;
  top: -0.2em;
  left: -1em;
  height: 1em;
}

aside li.collapsed > ul {
  display: none;
}

aside li.directory::before {
  content: "+";
}

aside li:not(.collapsed).directory::before {
  content: "-";
}

aside li.directory {
  cursor: pointer;
}

@media print {
  aside {
    visibility: hidden;
  }
}