使用伪类:after,:before 和 transform：scale() 实现
border-box{
position:relative;
}
.border-box:after{
content:”;
position:absolute;
bottom:0;
left:0;
width:100%;
border-top:1px solid #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);
}
}