*{
box-sizing:border-box;
-moz-box-sizing:border-box; /* Firefox */
-webkit-box-sizing:border-box; /* Safari */ /*设置的区域宽度用百分比固定为父元素的宽度对应的百分百，不会收到padding或是border把盒子撑大*/
}
*:before,*:after {
-webkit-box-sizing: border-box;
-moz-box-sizing: border-box;
box-sizing: border-box;
}