:first-of-type

dt {
  font-weight: bold;
}

dd {
  margin: 3px;
}

dd:first-of-type {
  border: 2px solid orange;
}

<dl>
  <dt>Vegetables:</dt>
  <dd>1. Tomatoes</dd>
  <dd>2. Cucumbers</dd>
  <dd>3. Mushrooms</dd>
  <dt>Fruits:</dt>
  <dd>4. Apples</dd>
  <dd>5. Mangos</dd>
  <dd>6. Pears</dd>
  <dd>7. Oranges</dd>
</dl>

:first-of-type {
  /* ... */
}

<h2>Heading</h2>
<p>Paragraph 1</p>
<p>Paragraph 2</p>

p:first-of-type {
  color: red;
  font-style: italic;
}

<article>
  <div>This `div` is first!</div>
  <div>This <span>nested `span` is first</span>!</div>
  <div>
    This <em>nested `em` is first</em>, but this <em>nested `em` is last</em>!
  </div>
  <div>This <span>nested `span` gets styled</span>!</div>
  <p>This `p` qualifies!</p>
  <div>This is the final `div`.</div>
</article>

article :first-of-type {
  background-color: pink;
}