Retina SASS mix-in

mixins.scss

@mixin retina($defaultPath, $retinaPath, $minSize) {
  
  @media (min-width: $minSize) {
    background-image: url($defaultPath);

    @media (-webkit-min-device-pixel-ratio: 1.5),
    (-o-min-device-pixel-ratio: 3/2),
    (min-device-pixel-ratio: 1.5) {
      background-image: url($retinaPath);
      background-size: image-width($defaultPath) image-height($defaultPath);
    }
  }
}