.foo-image-download {
  background-repeat: no-repeat;
  background-position: center center;
  background-image: url(../img/download.png);
  width: 25px;
  height: 25px;
  position: absolute;
  left: 6px;
  top: 6px;
  z-index: 999;  
}

.foo-image-download:hover {
  background-repeat: no-repeat;
  background-position: center center;
  background-image: url(../img/download_hover.png);
  width: 25px;
  height: 25px;      
}