使用伪类：after,:before和transform:scale()实现border-box{position:relative;}.border-box:after{content:'';位置：绝对；底部：0；左：0；宽度：100%；border-top:1pxsolid#ddd;}@media(-webkit-min-device-pixel-ratio:2),(min-device-pixel-ratio:2){.border-box:after{transform:scaleY(0.5);-webkit-transform:scaleY(0.5);}}@media(-webkit-min-device-pixel-ratio:3),(min-device-pixel-ratio:3){.border-box:after{transform:scaleY(0.3);-webkit-transform:scaleY(0.3);}}
