discourse/app/assets/stylesheets/vendor/font_awesome/_mixins.scss

// Mixins
// --------------------------

@mixin fa-icon-rotate($degrees, $rotation) {
  filter: progid:DXImageTransform.Microsoft.BasicImage(rotation=$rotation);
  -webkit-transform: rotate($degrees);
     -moz-transform: rotate($degrees);
      -ms-transform: rotate($degrees);
       -o-transform: rotate($degrees);
          transform: rotate($degrees);
}

@mixin fa-icon-flip($horiz, $vert, $rotation) {
  filter: progid:DXImageTransform.Microsoft.BasicImage(rotation=$rotation);
  -webkit-transform: scale($horiz, $vert);
     -moz-transform: scale($horiz, $vert);
      -ms-transform: scale($horiz, $vert);
       -o-transform: scale($horiz, $vert);
          transform: scale($horiz, $vert);
}