.signal {
    border: 3px solid #333;
    border-radius: 50px;
    height: 50px;
    left: 50%;
    margin: -25px 0 0 -25px;
    opacity: 0;
    position: absolute;
    top: 50%;
    width: 50px;

    animation: pulsate 1.2s ease-out;
    animation-iteration-count: infinite;
}

.late {
  animation-delay: .25s;
}

@keyframes pulsate {
    0% {
      transform: scale(.1);
      opacity: 0.0;
    }
    50% {
      opacity: 1;
    }
    100% {
      transform: scale(1.2);
      opacity: 0;
    }
}