<root>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<style type="text/css">
root, html {
display: block;
margin: 0; padding: 0;
}
root {
margin: 20px 0;
html {
background-color: green;
margin: 10px 0;
height: 100px;
</style>
</head>
</html>
</root>