.calculator {
    width: 250px;
    margin: 0 auto;
    text-align: center;
  }
  
  #display {
    width: 100%;
    margin-bottom: 10px;
    padding: 5px;
  }
  
  .buttons button {
    width: 50px;
    height: 50px;
    margin: 5px;
    font-size: 20px;
  }