media query for retina display

레티나디스플레이를 지원하는 미디어 쿼리

@media (-webkit-min-device-pixel-ratio: 2),
    (min--moz-device-pixel-ratio: 2),
    (-o-min-device-pixel-ratio: 2/1),
    (min-device-pixel-ratio: 2),
    (min-resolution: 192dpi),
    (min-resolution: 2dppx) {

}