body {
    font-family: sans-serif;
  }
  
  button {
    margin: 25px auto;
    margin-top: auto;
    margin-left: 25px;
    width: 150px;
    height: 150px;
    border-radius: 50%;
    border: none;
    overflow: hidden;
    opacity: 0;
    cursor: pointer;
  }
  button:focus {
    outline: none;
  }
  
  .control-panel {
    float: left;
    padding-top: 30px;
  }
  
  .traffic-light {
    float: left;
    margin: 30px 0;
    padding: 20px;
    width: 200px;
    height: 550px;
    background-color: #696969;
    border-radius: 40px;
  }
  
  .bulb {
    margin: 25px auto;
    width: 150px;
    height: 150px;
    background-color: #111;
    border-radius: 50%;
    transition: background 500ms;
  }