JSFiddle - React, Tailwind, and code Playground

HTML

<div><details><summary>Gnod</summary>
  <div><details><summary>Discovery</summary>
    <div>Gnoosic</div>
    <div>Gnovies</div>
    <div>Gnooks</div>
 </details></div>
 <div><details><summary>Maps</summary>
    <div>Music-Map</div>
    <div>Movie-Map</div>
    <div>Literature-Map</div>
 </details></div>
</details></div>

CSS

details > :not(summary) {
  padding-left: 2em;
}

details[open] > :not(summary) {
  border-left: 1px solid black;
}