@mixin device-pixel-ratio($ratio: 2, $min-dpi: 192dpi, $min-dppx: 2dppx) {
  @media only screen and (-webkit-min-device-pixel-ratio: $ratio),
  only screen and (min--moz-device-pixel-ratio: $ratio),
  only screen and (  -o-min-device-pixel-ratio: $ratio/1),
  only screen and (     min-device-pixel-ratio: $ratio),
  only screen and (             min-resolution: $min-dpi),
  only screen and (             min-resolution: $min-dppx) { 
    @content;
  }
}


@mixin device-pixel-ratio($ratio: 2, $min-dpi: 192dpi, $min-dppx: 2dppx) {
  @media only screen and (-webkit-min-device-pixel-ratio: $ratio),
  only screen and (min--moz-device-pixel-ratio: $ratio),
  only screen and (  -o-min-device-pixel-ratio: #{($ratio*10)}/10),
  only screen and (     min-device-pixel-ratio: $ratio),
  only screen and (             min-resolution: $min-dpi),
  only screen and (             min-resolution: $min-dppx) { 
    @content;
  }
}


Interpolate variable so it renders as a fraction
Interpolate variable so it renders as a fraction

Opera only accepts device-pixel-ratio values as fractions