.tree {
      --spacing: 1.5rem;
      --radius: 7.5px;

      margin-left: 160px;
    }

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

    .tree ul {
      margin-left: calc(var(--radius) - var(--spacing) - 20px);
      padding-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) / -2);
      left: -2px;
      width: calc(var(--spacing) + 2px);
      height: calc(var(--spacing) + 1px);
      border: solid #ddd;
      border-width: 0 0 2px 2px;
    }

    .tree summary {
      display: block;
      cursor: pointer;
    }

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

    .tree summary:focus {
      outline: none;
    }

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

    .tree li::after,
    .tree summary::before {
      content: '';
      display: block;
      position: absolute;
      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: #ddd;
    }

    .tree summary::before {
      z-index: 1;
      background: #09F url('expand-collapse.svg') 0 0;
    }

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