#cf {

  position:relative;

  height:100px;

  margin:0 auto;

}



#cf img {

  height: 100%;

  position:absolute;

  left:0;

  -webkit-transition: opacity 0.5s ease-in-out;

  -moz-transition: opacity 0.5s ease-in-out;

  -o-transition: opacity 0.5s ease-in-out;

  transition: opacity 0.5s ease-in-out;

}



#cf img.top:hover {

  opacity:0;

}