@mixin opacity ($value, $important: false) {
  $importantValue: null;
  @if $important {
    $importantValue: unquote("!important");
  }

  opacity: $value $importantValue;

  @if $value < 1 {
    $valueperc: $value*100;
    filter: alpha(opacity=#{$valueperc}) #{$importantValue};
  } @else {
    filter: none #{$importantValue};
  }
}

// -webkit-box-shadow still needed for Android 2.3 and 3.0, as well as iOS 5
@mixin box-shadow ($shadows...) {
  @include prefixer(box-shadow, $shadows, webkit spec);
}