<root>
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
 <style type="text/css">
 root, html, body {
  display: block;
  margin: 0; padding: 0;
 }
 root {
  margin: 10px 0;
 }
 html {
  background-color: lightgreen;
  margin: 20px 0;
 }
 body {
  background-color: green;
  margin: 40px 0;
  height: 100px;
 }
 </style>
</head>
<body>
</body>
</html>
</root>