.calculator {
    width: 250px;
    margin: 50px auto;
    text-align: center;
  }
  
  #display {
    width: 100%;
    height: 40px;
    margin-bottom: 10px;
  }
  
  .keys button {
    width: 50px;
    height: 50px;
    margin: 5px;
    font-size: 20px;
  }
  
  .keys {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
  }

  .code-box{
    background-color: #101010;

}

.code-box{
    font: 30px;
    color: #fff;
}