<html>
<link rel="stylesheet" href="seamless-iframe.css">
<body>
<iframe src="/slow?100" id="frame" class="seamless"></iframe>
<script>
let frame = document.getElementById("frame");
let doc = frame.contentDocument;
doc.open();
doc.write("<html>Rewritten. <img src=pixel.png> </html>");
doc.close();
</script>
</body>
</html>