如何在css中添加一个接一个的脉冲动画，如红绿灯不断闪烁

<div class="traffic-light"></div>

.traffic-light {
  width: 40px;
  height: 120px;
  background-color: black;
  position: relative;
}

.traffic-light::before,
.traffic-light::after {
  content: "";
  width: 40px;
  height: 40px;
  border-radius: 50%;
  position: absolute;
  top: 10px;
  left: 50%;
  transform: translateX(-50%);
  animation-duration: 1s;
  animation-iteration-count: infinite;
}

.traffic-light::before {
  background-color: red;
  animation-name: pulse-red;
}

.traffic-light::after {
  background-color: green;
  animation-name: pulse-green;
  animation-delay: 0.5s;
}

@keyframes pulse-red {
  0% {
    box-shadow: 0 0 0 0px red;
  }
  50% {
    box-shadow: 0 0 0 20px red;
  }
  100% {
    box-shadow: 0 0 0 0px red;
  }
}

@keyframes pulse-green {
  0% {
    box-shadow: 0 0 0 0px green;
  }
  50% {
    box-shadow: 0 0 0 20px green;
  }
  100% {
    box-shadow: 0 0 0 0px green;
  }
}