<main>
  <div>I am `div` #1.</div>
  <p>I am the only `p` among my siblings.</p>
  <div>I am `div` #2.</div>
  <div>I am `div` #3.
    <i>I am the only `i` child.</i>
    <em>I am `em` #1.</em>
    <em>I am `em` #2.</em>
  </div>
</main>
body{
  background: #1f1f1f;
  width: 80%;
  border: 1px dashed #ffffff;
  margin: auto;
  padding: 50px;
  color: #ffffff;
}

/* only-of-type selector */
 main :only-of-type {
  color: red;
}

External CSS

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