gistfile1.css

@media only screen and (min--moz-device-pixel-ratio: 1.5), /* Gecko */
       only screen and (-o-min-device-pixel-ratio: 3/2), /* Opera */
       only screen and (-webkit-min-device-pixel-ratio: 1.5), /* Webkit */
       only screen and (min-device-pixel-ratio: 1.5), /* Webkit */
       only screen and (min-resolution: 144dpi) /* W3 */
       {
	.button-icon {
		background-image: url("path/to/image/name@2x.png");
		background-size: 16px 16px;
	}
}