<!DOCTYPE html>
<html>
<head>
<style>
div#x::first-letter { color: blue; }
</style>
</head>
<body>
<div id="x">x</div>
<script>
document.body.offsetWidth;
var div = document.getElementById("x");
div.id = "y";
div.firstChild.remove();
</script>
</body>
</html>