圣杯布局和双飞翼布局的特点:
圣杯布局和双飞翼布局的实现方式:
圣杯布局
this is headerthis is centerthis is leftthis is rightthis is footer
效果

双飞翼布局
this is mainthis is leftthis is right
效果

clearfix可以用于清除浮动,加在浮动的元素上
.clearfix:after{content: '';display: table;clear: both;
}