单伪元素方法：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
.clearfix:after{
content:"";
height:0;
lin-height:0;
display:block;
visibility:hidden;
clear:both;
}
.clearfix:after{
*zoom:1; /*针对IE6/IE7*/
}
</style>
</head>
<body>
</body>
</html>双伪元素方法：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
.clearfix:before,.clearfix:after{
content:"";
display:table;
}
.clearfix:after{
clear:both;
}
.clearfix:after{
*zoom:1;
}
</style>
</head>
<body>
</body>
</html>