Background image for retina screens

background.css

background-color: transparent;
background-size: 100px 100px;
background-repeat: no-repeat;
background-position: top center;
background-image: url("bg.png");

@media
only screen and (-webkit-min-device-pixel-ratio: 2),
only screen and (   min--moz-device-pixel-ratio: 2),
only screen and (     -o-min-device-pixel-ratio: 2/1),
only screen and (        min-device-pixel-ratio: 2),
only screen and (                min-resolution: 192dpi),
only screen and (                min-resolution: 2dppx) {
    background-image: url("[email protected]");
}

@media
only screen and (-webkit-min-device-pixel-ratio: 3),
only screen and (   min--moz-device-pixel-ratio: 3),
only screen and (     -o-min-device-pixel-ratio: 3/1),
only screen and (        min-device-pixel-ratio: 3),
only screen and (                min-resolution: 384dpi),
only screen and (                min-resolution: 3dppx) {
    background-image: url("[email protected]");
}