<!DOCTYPE html>
<!-- Any copyright is dedicated to the Public Domain.
   - http://creativecommons.org/publicdomain/zero/1.0/ -->

<html>
  <style>
  summary {
    display: table-cell;
  }
  </style>
  <body>
    <details open>
      <p>This is the details.</p>
      <!-- Make summary the second element child so that layout will try to
           render it as the first child. -->
      <summary>Summary
        <div>Block in summary</div>
      </summary>
    </details>
  </body>
</html>