#btn_bec  img {display: none;}
#btn_bec{
  display: block;
  width:250px;
  height:60px;
  background-image:url(img/btn_bec.jpg);
}
#btn_bec:hover {
  display: block;
  width:250px;
  height:60px;
  background-image:url(img/btn_bec_hover.jpg);
}