JSFiddle - React, Tailwind, and code Playground

HTML

<nav>
    <ul>
      <li>Lv1: First Item</li>
      <li>Lv1: Second Item</li>
      <li>
        <ul>
          <li>Lv2: First Item</li>
          <li>
            <ul>
              <li>Lv3: First Item</li>
              <li>Lv3: Second Item</li>
              <li>Lv3: Third Item</li>
            </ul>
          </li>
          <li>Lv2: Second Item</li>
          <li>Lv2: Third Item</li>
        </ul>
      </li>
    </ul>
</nav>

CSS

ul > li:hover {
    background: yellow;
}
ul > li:hover > ul {
    background: white;
}