CSS: How do I create a button with pulse effect?

.button {
  width: 130px;
  height: 130px;
  text-transform: uppercase;
  letter-spacing: 1px;
  color: #fff;
  text-align: center;
  background: rgba(30, 144, 255, 0.6);
  border-radius: 50%;
  animation: shadow-pulse 1s infinite;
}

@keyframes shadow-pulse
{
  0% {
    box-shadow: 0 0 0 0px rgba(0, 0, 0, 0.2);
  }
  100% {
    box-shadow: 0 0 0 35px rgba(0, 0, 0, 0);
  }
}