.traffic-light {
  margin-top: 30px;
  width: 200px;
  height: 200px;
  border: 1px solid black;
  border-radius: 50%;
}

.traffic-light_red {
  background-color: red;
}
.traffic-light_yellow {
  background-color: yellow;
}
.traffic-light_green {
  background-color: green;
}