<html>
<style>
body { font-size: 1px; }
div { width: 5rem; height:100px; background: green; }
</style>
<body>
<div>
<span></span>
</div>
<script>
document.querySelector('div').isContentEditable;
document.querySelector('span').focus();
document.querySelector('html').style.fontSize = '20px';
</script>