<!doctype html>
<html>
<head>
<style type="text/css" media="screen">
     #greenBox {
        width:200px;
        height:100px;
        display:block;
        background-color: green;
        float: left;
    }
</style>
</head>
<body>
<div id="greenBox"></div>
</body>
</html>