0px;
      }

      ul,
      li {
        list-style: none;
        margin: 0;
        padding: 0;
      }

      ul {
        padding-left: 14px;
      }

      li {
        padding-left: 10px;
        border: 1px solid silver;
        border-width: 0 0 1px 1px;
      }

      li.has-children {
        border-bottom: 0px;
      }

      li ul {
        margin-left: -10px;
        padding-left: 20px;
      }
    </style>
    <div id="tree"></div>
  </template>
  <script>
    class TreeView extends Polymer.