a[href="#popup:myform"]{
 animation: animate_pulse 1.5s infinite;
}
@keyframes animate_pulse {
 0% {
 box-shadow: 0 0 0 0 rgba(53, 79, 82, 0.4);
 }
 70% {
 box-shadow: 0 0 0 10px rgba(53, 79, 82, 0);
 }
 100% {
 box-shadow: 0 0 0 0 rgba(53, 79, 82, 0);
 }
}