basic retina / high res media query

retina_media_query.css

@media (min--moz-device-pixel-ratio: 1.5),
       (-o-min-device-pixel-ratio: 3/2),
       (-webkit-min-device-pixel-ratio: 1.5),
       (min-resolution: 1.5dppx) {

       #selector {
         background-image: url(image@2x.png);
         background-size: 15px auto; /* example */
       }
}