body {
    font-family: 'Dejavu Sans Mono', 'Arial', sans-serif;
}

* {
    margin: 0;
    padding: 0;
}

.tree-html ul {
    margin-left: 15px;
}

.tree-html li {
    list-style-type: none;
    margin: 10px;
    position: relative;
}

.tree-html li::before {
    content: "";
    position: absolute;
    top: -7px;
    left: -15px;
    border-left: 1px dotted #ccc;
    border-bottom: 1px dotted #ccc;
    width: 15px;
    height: 15px;
}

.tree-html li::after {
    position: absolute;
    content: "";
    top: 8px;
    left: -15px;
    border-left: 1px dotted #ccc;
    width: 15px;
    height: 100%;
}

.tree-html li:last-child::after {
    display: none;
}

ul.tree-html>li:first-child::before {
    display: none;
}

.tree-html li a {
    padding: 2px 5px;
}

.tree-html li a:hover, .tree-html li a:hover+ul li a,
.tree-html li a:focus, .tree-html li a:focus+ul li a {
    background: gray;
}

.tree-html label {
  margin: 0 0 0 5px;
  border: 1px solid #ccc;
  width: .6em;
  height: .6em;
  display: inline-block;
  line-height: .65;
}

.tree-html label::before {
  color: #ccc;
  font-family: serif;
  margin-left: 0.02em;
}

input[type='checkbox'] {
  margin-left: 5px;
  display: none
}

input[type='checkbox']:checked ~ ul {
  display: none
}

input[type="checkbox"] + label::before {
  content: '-';
}

input[type="checkbox"]:checked + label::before {
  content: '+';
}