<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html" charset="utf-8" />
<title>Div Middle</title>
<style>
span{width:100px;height:100px;background:red;float:left}
</style>
</head>
<body>
<span></span>
</body>
</html>
原文：http://www.cnblogs.com/hduhdc/p/5493098.html