=rgba($foreground, $backdrop: white, $property: "background-color")
  #{$property}: mix(fade-in($foreground, 1), $backdrop, percentage(opacity($foreground)))
  // Browsers without color opacity
  #{$property}: $foreground
  // Decent browsers
  #{$property}: mix(fade-in($foreground, 1), $backdrop, percentage(opacity($foreground)))\9
  // IE8
  @if $property == "background-color"
    +rgba-background($foreground)