Font-Awesome/scss/_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, $vert) {
  -webkit-transform: scale($horiz, $vert);
     -moz-transform: scale($horiz, $vert);
      -ms-transform: scale($horiz, $vert);
       -o-transform: scale($horiz, $vert);
          transform: scale($horiz, $vert);
}

@mixin fa-icon-stack($width: 2em, $height: 2em, $top-font-size: 1em, $base-font-size: 2em) {
  .#{$fa-css-prefix}-stack {
    position: relative;
    display: inline-block;
    width: $width;
    height: $height;
    line-height: $width;
    vertical-align: -35%;
    .#{$fa-css-prefix} {
      position: absolute;
      display: block;
      width: 100%;
      height: 100%;
      font-size: $top-font-size;
      line-height: inherit;
      text-align: center;
    }
    .#{$fa-css-prefix}-stack-base {
      font-size: $base-font-size;
    }
  }
}