JSFiddle - React, Tailwind, and code Playground

HTML

<ul>
  <li>Item 1</li>
  <li>Item 2</li>
  <li>Item 3</li>
</ul>

<ul>
  <li>Item 1
    <ul>
      <li>Item 1-1
        <ul>
          <li>Item 1-1-1</li>
        </ul>
      </li>
    </ul>
  </li>
</ul>

CSS

:not(li) ul:not(:has(ul)) {
  background-color: tomato;
}