HTML Code

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <title>article header demo</title>
  <style>
    body { font-family: sans-serif; padding: 16px; max-width: 32rem; }
    article, aside { padding: 12px; margin: 8px 0; border: 1px solid #e2e8f0; border-radius: 6px; }
  </style>
</head>
<body>
  <article>
    <h2>Article Title</h2>
    <p>Main content here.</p>
    <h3>Section</h3>
  </article>
  <aside>
    <h4>Related</h4>
    <p>Sidebar heading unchanged.</p>
  </aside>
  <script src="https://code.jquery.com/jquery-3.7.1.min.js"></script>
  <script>
    $("article :header").css("borderLeft", "4px solid #2563eb");
  </script>
</body>
</html>

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article :header — scoped headings (Try It)