.tree {
  --spacing: 1.5rem;
  --radius: 10px;
  --item-padding: 0.5em;
  --line-color: #ddd;
  --expand-item: #444 url('img/expand-collapse.svg') 0 0;
}

.tree li {
  display: block;
  position: relative;
  padding-left: calc(2 * var(--spacing) - var(--radius) - 2px);
}

.tree ul {
  margin-left: calc((-1 * var(--spacing) + 2px));
  margin-top: 0;
}
.tree ul.level0{
	margin-left: 0;
}

.tree ul li {
  border-left: 2px solid #ddd;
}

.tree ul li:last-child {
  border-color: transparent;
}

.tree ul li::before {
  content: '';
  display: block;
  position: absolute;
  top: calc((var(--spacing) - var(--item-padding)) / -2);
  left: -2px;
  width: calc(var(--spacing) + 2px);
  height: calc(var(--spacing) + 1px);
  border: solid var(--line-color);
  border-width: 0 0 2px 2px;
}

.tree summary {
  display: block;
  cursor: pointer;
  padding: var(--item-padding) 0;
  display:flex;
  margin-left: -1em;
}

.tree summary::marker,
.tree summary::-webkit-details-marker {
  display: none;
}

.tree summary:focus {
  outline: none;
}

.tree summary:focus-visible {
  outline: 1px dotted #000;
}

.tree summary::before {
  content: '';
  display: block;
  top: calc(var(--spacing) / 2 - var(--radius));
  left: calc(var(--spacing) - var(--radius) - 1px);
  width: calc(2 * var(--radius));
  height: calc(2 * var(--radius));
  border-radius: 50%;
  background: var(--line-color);
  margin-right: 0.3em;
}

.tree summary.children::before {
  z-index: 1;
  background: var(--expand-item);
}

.tree details[open] > summary::before {
  background-position: calc(-2 * var(--radius)) 0;
}