/* Keep the original callback images and show exactly one viewport variant. */
.call_back.cb_d{display:block;visibility:visible}
.call_back.cb_m{display:none;visibility:hidden}
@media(max-width:780px){
 .call_back.cb_d{display:none;visibility:hidden}
 .call_back.cb_m{display:block;visibility:visible}
}