清除浮动业内最高尚的办法 :before :after 伪类

.clearfix:before,/*清除浮动 display:flex可代替float*/
.clearfix:after{
content: " ";
display: block;
height: 0;
clear: both;
visibility: hidden;
}
.clearfix:after{
clear: both;
}

最优雅
.clearfix:before,
.clearfix:after{
content: " ";
display: table;
}
.clearfix:after{
clear: both;
}

em rem
100% 1em=16px