.clear 万能清除浮动(clearfix:after)

html body div.clear,
html body span.clear
{
background: none;
border: 0;
clear: both;
display: block;
float: none;
font-size: 0;
margin: 0;
padding: 0;
overflow: hidden;
visibility: hidden;
width: 0;
height: 0;
}

.clearfix:after {
content: "020";
display: block;
height: 0;
clear: both;
}
.clearfix {
zoom: 1;
}