Retina mixin

retina.scss

$isRetina: "(-webkit-min-device-pixel-ratio: 1.5), (min--moz-device-pixel-ratio: 1.5), (-o-min-device-pixel-ratio: 3/2), (min-device-pixel-ratio: 1.5)";
 
@mixin retina {
  @media #{$isRetina} { @content; }
}
 
 
// usage
.logotype {
  width: 100px;
  height: 50px;
  background-image: url('path/to/image.png');
 
  @include retina {
    background-image: url('path/to/retina/image.png');
    background-size: 100px 50px;
  }
}