<!DOCTYPE html>
<html>
<head>
<style type="text/css">
#float-blue {
 float: left;
 margin: 0 20px;
 background-color: green;
 width: 40px;
 height: 100px;
}
.float-green {
 float: left;
 background-color: green;
 width: 40px;
 height: 100px;
}
</style>
</head>
<body>
<div id="float-blue"></div><div class="float-green"></div>
</body>
</html>