css/css-multicol/multicol-span-all-006.html

<!DOCTYPE html>
<html>
  <meta charset="utf-8">
  <title>CSS Multi-column Layout Test: Test column-span:all under HTML details tag</title>
  <link rel="author" title="Ting-Yu Lin" href="mailto:tlin@mozilla.com">
  <link rel="author" title="Mozilla" href="http://www.mozilla.org/">
  <link rel="help" href="https://drafts.csswg.org/css-multicol-1/#column-span">
  <link rel="match" href="multicol-span-all-006-ref.html">
  <meta name="assert" content="This test checks a column-span:all element is working under HTML details tag.">

  <style>
  details {
    column-count: 3;
    column-rule: 6px solid;
    width: 400px;
    outline: 1px solid black;
  }
  h3 {
    column-span: all;
    outline: 1px solid blue;
  }
  </style>

  <body>
    <details open>
      <summary>Columns</summary>
      <h3>spanner</h3>
      <div>block</div>
    </details>
  </body>
</html>