@mixin retina-img($file-1x, $file-2x, $size) {
  background-image: $file-1x;

  // prettier-ignore
  @media only screen and (min-resolution: 192dpi), only screen and (min-resolution: 2dppx) {
    background-image: $file-2x;
    background-size: $size;
  }
}