清除浮动 --- 目前使用范围最广的方法
.clearfix:before,.clearfix:after{
display: table;
content: "";}
.clearfix:after {
clear: both;}
.clearfix {
zoom: 1;}
.clearfix:before,.clearfix:after{
display: table;
content: "";}
.clearfix:after {
clear: both;}
.clearfix {
zoom: 1;}