.overlay-ajax{
  position: fixed;
  z-index: 999999;
  width: 100%;
  height: 100%;
  top: 0;
  left: 0;
  opacity: 0;
  visibility: hidden;
  -webkit-transition: all ease 0.5s;
  -ms-transition: all ease 0.5s;
  -o-transition: all ease 0.5s;
  -moz-transition: all ease 0.5s;
  background: rgba(255, 255, 255, 0.72) url('../css/preloader.gif') no-repeat center center;
}
 
.overlay-ajax.active{
  opacity: 1;
  visibility: visible;
}