nested-media-queries.scss

@mixin mq($mq) {
  @if $mq == 690  { @media (max-width: 690px)  { @content; } }
  @if $mq == 320  { @media (max-width: 320px)  { @content; } }

  @if $mq == retina {
    @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) {
        @content;
    }
  }
}