<html>
<head>
<style>
div { background-color: red; width: 100px; height: 100px }
</style>
</head>
<script>
var s = document.createElement("style");
var t = document.createTextNode("div { background-color: green }");
s.appendChild(t);
document.documentElement.appendChild(s);
</script>
<style>
div { background-color: orange }
</style>
You should see a 100x100 green square below.  If you see any red or orange then the test has failed.
<div></div>
</html>