<html>
<head>
<body>
    <div id="inline-block" style="display: inline-block">
      HELLO WORLD
    </div>
    <div id="grid" style="display: grid"></div>
    <div id="block" style="position: fixed"></div>
    <script>
       "use strict";

       window.onload = () => {
         window.opener.postMessage("ready", "*");
       };
     </script>
</body>
</html>
