伪元素清除浮动

.clearfix:after{
content: '.';
display: block;
height: 0;
line-height: 0;
visibility: hidden;
clear: both;
}
.clearfix{
zoom: 1;
}

.clearfix:before,.clearfix:after{
content: '';
display: table;
}
.clearfix:after{
clear: both;
}
.clearfix{
zoom: 1; /*兼容ie*/
}