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

<html>
  <style>
  body {
    width: 400px;
  }
  div#float {
    float: left;
    width: 200px;
    height: 400px;
    background-color: lightgreen;
  }
  details {
    float: left;
    background-color: orange;
  }
  summary {
    background-color: green;
    /* Hide the triangle for comparing with div in reftest. */
    list-style-type: none;
  }
  </style>
  <body>
    <details open>
      <summary>Summary</summary>
      <div id="float"></div>
    </details>
  </body>
</html>