<ul>
  <li>1</li>
  <li> </li>
  <li></li>
  <li>4</li>
  <li><div>5</div></li>
  <li><div></div></li>
</ul>
li {
  height: 20px;
  background: yellow;
}

div {
  height: 20px;
  background: gold;
}

*:empty {
  background: pink;
}

External CSS

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External JavaScript

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