<section>
  <h2>見出し</h2>
  <ul>
    <li>タグ1</li><li>タグ2</li><li>タグ3</li>
  </ul>
</section>
<section>
  <h2>見出し</h2>
  <ul>
    <li>タグ1</li>
  </ul>
</section>
<section>
  <h2>見出し</h2>
  <ul>
    <li>タグ1</li><li>タグ2</li>
  </ul>
</section>
section ul li:only-child {
  color: #ff0000;
}

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External JavaScript

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