Collapsible File Tree

<!--
  Static two-level snapshot; the React/TypeScript tabs add expand/collapse and
  arbitrary depth. role="tree" + treeitem + group and aria-expanded are what make
  this a tree to a screen reader, not just an indented list. min-w-0 + truncate
  on every label is what stops deep nesting scrolling the page at 320px.
-->
<nav class="w-full max-w-sm rounded-xl border border-gray-200 bg-white p-2 text-sm text-gray-700 dark:border-gray-800 dark:bg-gray-950 dark:text-gray-300">
  <ul role="tree" aria-label="Project files" class="space-y-0.5">
    <li role="treeitem" aria-expanded="true">
      <button type="button" class="flex w-full min-w-0 items-center gap-1.5 rounded-md px-2 py-1.5 text-left hover:bg-gray-100 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-blue-500 dark:hover:bg-gray-900">
        <svg viewBox="0 0 16 16" fill="currentColor" class="h-3.5 w-3.5 shrink-0 rotate-90 text-gray-400" aria-hidden="true"><path d="M6 4l4 4-4 4z"/></svg>
        <svg viewBox="0 0 16 16" fill="currentColor" class="h-4 w-4 shrink-0 text-blue-500" aria-hidden="true"><path d="M1.5 4A1.5 1.5 0 0 1 3 2.5h3L7.5 4H13A1.5 1.5 0 0 1 14.5 5.5v6A1.5 1.5 0 0 1 13 13H3a1.5 1.5 0 0 1-1.5-1.5z"/></svg>
        <span class="truncate font-medium text-gray-900 dark:text-gray-100">src</span>
      </button>
      <ul role="group" class="ml-3 space-y-0.5 border-l border-gray-200 pl-2 sm:ml-4 dark:border-gray-800">
        <li role="treeitem">
          <span class="flex min-w-0 items-center gap-1.5 rounded-md px-2 py-1.5 hover:bg-gray-100 dark:hover:bg-gray-900">
            <span class="w-3.5 shrink-0" aria-hidden="true"></span>
            <svg viewBox="0 0 16 16" fill="currentColor" class="h-4 w-4 shrink-0 text-gray-400" aria-hidden="true"><path d="M4 1.5h4.6L13 5.9V14a.5.5 0 0 1-.5.5h-8A.5.5 0 0 1 4 14V2a.5.5 0 0 1 .5-.5z"/></svg>
            <span class="truncate">index.ts</span>
          </span>
        </li>
      </ul>
    </li>
    <li role="treeitem">
      <span class="flex min-w-0 items-center gap-1.5 rounded-md px-2 py-1.5 hover:bg-gray-100 dark:hover:bg-gray-900">
        <span class="w-3.5 shrink-0" aria-hidden="true"></span>
        <svg viewBox="0 0 16 16" fill="currentColor" class="h-4 w-4 shrink-0 text-gray-400" aria-hidden="true"><path d="M4 1.5h4.6L13 5.9V14a.5.5 0 0 1-.5.5h-8A.5.5 0 0 1 4 14V2a.5.5 0 0 1 .5-.5z"/></svg>
        <span class="truncate">package.json</span>
      </span>
    </li>
  </ul>
</nav>