How to fix incorrect display of nested grouping symbol. "Details" Tag?

If the top level is raised, all household levels are assigned. "-" Symbol, even if they collapse: jsfiddle.net/acces969/4eh6puvk/1/

<div class="treeHTML">Root
  <div>level 1
    <details><summary></summary>
      <div >level 2
        <details><summary></summary>
          <div >
            level 3
          </div>
        </details>
      </div>
    </details>
  </div>
</div>