sanhai,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<style type="text/css">
.m {
background-color: #FF0000;
}
body, html {
width: 100%;
height: 100%;
}
</style>
</head>
<body>
<div class="m" id="immm"></div>
<script>
document.styleSheets[0].insertRule("#immm { width: 100%; height: 100%; }", 0);
</script>
</body>
</html>