* {
    box-sizing: border-box;
  }
  
  body {
    font-family: 'Roboto', Arial, sans-serif;
    background-color: #f7f7f7;
    margin: 0;
    padding: 0;
  }
  
  .calculator {
    max-width: 360px;
    margin: 50px auto;
    background-color: #333333;
    border-radius: 8px;
    padding: 20px;
  }
  
  #display {
    width: 100%;
    height: 60px;
    margin-bottom: 20px;
    font-size: 28px;
    text-align: right;
    padding: 10px;
    border: none;
    background-color: #191919;
    color: #ffffff;
    border-radius: 4px;
    outline: none;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
  }
  
  .buttons {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(80px, 1fr));
    margin-top: 10px;
  }
  
  button {
    width: 90%;
    margin-bottom: 8px;
    height: 60px;
    font-size: 24px;
    border: none;
    background-color: #454545;
    color: #ffffff;
    cursor: pointer;
    outline: none;
    border-radius: 4px;
    transition: background-color 0.2s ease;
  }
  
  button.operator {
    background-color: #ff9f00;
    color: #ffffff;
  }
  
  button:hover {
    background-color: #606060;
  }