// Set HiDPI (Retina) image sizes and background.
//
//   .button
//      +hidpi-image("nice/button.png")
@mixin hidpi-image($path)
  +image-size($path, 2)
  background: image-url($path) no-repeat
  background-size: (image-width($path) / 2) (image-height($path) / 2)