* {
    box-sizing: border-box;
  }
  
  body {
    padding: 0;
    margin: 0;
  }

  .calculator {
      background-color: black;
      width: 400px;
      height: 600px;
      color: white;
  }

  .head {
      height: 100px;
      padding-top: 25px;
      padding-right: 5px;
      text-align: right;
      font-size: 40px;
  }
  .button {
    font-size: 30px;
    background-color: #bcbdbe;
    height: 100px;
  
    width: 25%
      
  }

  .button:last-child {
      color: white;
      background-color: #df974c;
  }
  .button.big {
     width: 50%;
  }
  .button.large {
      width: 75%;
  }
.row {
  display: flex;
  align-content: stretch;
}
.button:hover {
    background-color: #dedfe0;
}
.button:last-child:hover {
    background-color: #f7c590;
}