body {
    font-family: 'Arial', sans-serif;
    background-color: #f7f7f7;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
  }
  
  .calculator {
    background-color: #fff;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.2);
  }
  
  #display {
    width: 100%;
    font-size: 2em;
    text-align: right;
    margin-bottom: 10px;
    padding: 10px;
    border: 2px solid #ddd;
    border-radius: 5px;
  }
  
  .buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
  }
  
  .btn {
    font-size: 1.5em;
    padding: 20px;
    border: none;
    background-color: #007bff;
    color: white;
    border-radius: 5px;
    cursor: pointer;
  }
  
  .btn.operator {
    background-color: #f39c12;
  }
  
  #clear {
    background-color: #e74c3c;
  }
  
  #equals {
    background-color: #2ecc71;
  }
  
  .btn:hover {
    opacity: 0.8;
  }