animate.css/source/attention_seekers/pulse.css

/* originally authored by Nick Pettit - https://github.com/nickpettit/glide */

@keyframes pulse {
  0% {
    transform: scale(1);
  }

  50% {
    transform: scale(1.1);
  }

  100% {
    transform: scale(1);
  }
}

.pulse {
  animation-name: pulse;
}