.box:after{
content: ".";
display:block;
height:0;
clear:both;
overflow:hidden;
visibility:hidden;
}
.box
即是需要解决高度塌陷问题的父元素的类名
.box:after{
content: ".";
display:block;
height:0;
clear:both;
overflow:hidden;
visibility:hidden;
}
.box
即是需要解决高度塌陷问题的父元素的类名