<!DOCTYPE html>
<html>
<head>
<style type="text/css">
#float {
 width: 100px; height: 100px;
 background-color: blue;
}
#separator {
 margin-top: 30px;
 height: 20px;
 width: 100%;
 background-color: green;
}
</style>
</head>
<body>
<div id="float"></div>
<div id="separator"></div>
There should be gap between the blue square and the green rectangle.
</body>
</html>