source/font-awesome/less/mixins.less

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

.fa-icon() {
  display: inline-block;
  font: normal normal normal @fa-font-size-base/1 FontAwesome; // shortening font declaration
  font-size: inherit; // can't have font-size inherit on line above, so need to override
  text-rendering: auto; // optimizelegibility throws things off #1094
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  transform: translate(0, 0); // ensures no half-pixel rendering in firefox

}

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

.fa-icon-flip(@horiz, @vert, @rotation) {
  filter: progid:DXImageTransform.Microsoft.BasicImage(rotation=@rotation, mirror=1);
  -webkit-transform: scale(@horiz, @vert);
      -ms-transform: scale(@horiz, @vert);
          transform: scale(@horiz, @vert);
}