chromium/content/test/data/accessibility/event/add-dialog-no-info.html

<html>
  <head>
      <script>
          function go() {
            document.getElementById("no-info-dialog").removeAttribute("hidden");
          }
      </script>
  </head>
  <body>

    <div id="no-info-dialog" role="dialog" hidden>
      <h2>Dialog title</h2>
      <p>Dialog content:</p>
      <div>
        <input type="text" id="no-info-dialog-focus-element">
      </div>
    </div>

  </body>
</html>