style.css

* {
  box-sizing: border-box;
}

body {
  font-family: "Bubblegum Sans", cursive, sans-serif;
  display: flex;
  flex-direction: column;
  align-items: center;
  background-color: #8cd8e6;
  color: midnightblue;
  font-size: 20px;
}

.btn {
  font-size: 15px;
  color: midnightblue;
  width: 150px;
  padding: 6px;
  border-radius: 15px;
  background-color: cyan;
  box-shadow: 5px 5px 10px mediumblue;
}

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

.traffic-light_red {
  background-color: red;
  box-shadow: 5px 10px 10px red, 5px 15px 15px crimson, 1px 10px 5px midnightblue inset, 5px 5px 5px white inset, 5px 5px 5px white inset;
}

.traffic-light_yellow {
  background-color: yellow;
  box-shadow: 5px 10px 10px yellow, 5px 15px 15px yellowgreen, 1px 10px 5px midnightblue inset, 5px 5px 5px white inset, 5px 5px 5px white inset;
}

.traffic-light_green {
  background-color: green;
  box-shadow: 5px 10px 10px green, 5px 15px 15px limegreen, 1px 10px 5px midnightblue inset, 5px 5px 5px white inset, 5px 5px 5px white inset;
}