.keypad .btn {
      width: 60px;
      height: 60px;
      font-size: 24px;
      margin: 5px;
    }
    .keypad {
      max-width: 220px;
      margin: 0 auto;
    }
    #codeDisplay {
      font-size: 1.5rem;
      letter-spacing: 0.4rem;
    }