CSS - Transitions with Sprites

css_tranistions_sprites.css

.icon-facebook { 
  background-position: -50px 0;
  width: 20px; 
  height: 19px; 
  position: relative;
  text-indent: -9999px;
  display: inline-block;
} 
.icon-facebook:after{ 
  background: url("images/sprites/sprite-icons.png") no-repeat scroll -75px 0 transparent;
  bottom: 0;
  content: "";
  left: 0;
  opacity: 0;
  position: absolute;
  right: 0;
  top: 0;
  -webkit-transition: opacity .5s ease 0s;
     -moz-transition: opacity .5s ease 0s;
      -ms-transition: opacity .5s ease 0s;
       -o-transition: opacity .5s ease 0s;
          transition: opacity .5s ease 0s;
}