Media query for retina display
@media
only screen and (-webkit-min-device-pixel-ratio: 2),
only screen and ( -moz-min-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) {
/* styles */
}