PC端不同屏幕使用不同倍数的icon

css样式
`
.bg-image(@url){

background-image:~"url(@{url}@2x.png)";

@media(-webkit-min-device-pixel-ratio:3),(min-device-pixel-ratio:3){

	background-image:~"url(@{url}@3x.png)";

}

@media(-webkit-min-device-pixel-ratio:4),(min-device-pixel-ratio:4){

	background-image:~"url(@{url}@4x.png)";

};

background-repeat:no-repeat;

background-size:100% 100%;

-moz-background-size:100% 100%;

}
`