CSS: Retina Media Queries

// Simple
@media 
(-webkit-min-device-pixel-ratio: 2), 
(min-resolution: 192dpi) { 
    /* Retina-specific stuff here */
}

// Future Proof
@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) { 
  
  /* Retina-specific stuff here */

}