.advert-photo.virtual-iframe a {
  position: relative;
}
.advert-photo.virtual-iframe a:after { 
  opacity: 0.7;
  content: ' ';
  display: block;
  top: 0;
  bottom: 0;
  left: 0;
  right: 0;
  position: absolute;
  background: url('https://www.crdb.cz/_css/virtual_play.png') 50% 50% no-repeat;
  background-size: 40%;
}
.advert-photo.virtual-iframe.virtual-360 a:after,
.advert-photo.virtual-iframe.virtual-3D a:after {
  background-image: url('https://www.crdb.cz/_css/virtual_360.png'); 
  background-size: 60%;
  opacity: 1;
}
.advert-photo.virtual-iframe a:hover:after {
  opacity:1;
}
.advert-photo.virtual-iframe.virtual-360 a:hover:after {
  opacity:0.7;
} 