traffic_light.css

* {
  box-sizing: border-box;
}

body,
html {
  margin: 0;
  padding: 0;
}

.outer {
  width: 20%;
  margin: 0;
  border: 1px solid #000;
  padding: 2.5vw;
  z-index: 200;
  border-radius: 5px;
}

.inner {
  background-color: #000;
  padding: 2.5vw;
  border-radius: 5px;
}

.light {
  background-color: #ccc;
  width: 10vw;
  height: 10vw;
  margin-bottom: 10px;
  border-radius: 50%;
}

.light:last-child {
  margin-bottom: 0;
}

.stop.on {
  background-color: #f00;
}

.caution.on {
  background-color: #ff0;
}

.go.on {
  background-color: #0f0;
}

.container {
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  align-items: center;
  height: 100vh;
}

header {
  width: 100%;
  background-color: #eee;
  padding: 15px;
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
}

footer {
  width: 100%;
  background-color: #eee;
  padding: 15px;
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
}

footer button,
header button {
  background-color: #eee;
  padding: 15px;
  border-radius: 5px;
  margin-inline-end: 5px;
}

button#stop {
  background-color: red;
  color: white;
}

button#caution {
  background-color: yellow;
}

button#go {
  background-color: green;
  color: white;
}