body {
    font-family: 'Arial', sans-serif;
    background: #898989;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
  }
  
  .calculator {
    background: #fff;
    border-radius: 12px;
    box-shadow: 0 0 15px rgba(0,0,0,0.1);
    width: 320px;
    overflow: hidden;
  }
  
  .display {
    background: #222;
    color: #0f0;
    font-size: 2rem;
    text-align: right;
    padding: 20px;
    height: 70px;
    overflow-x: auto;
  }
  
  .buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 1px;
    background: #ccc;
  }
  
  .btn {
    padding: 20px;
    font-size: 1.5rem;
    border: none;
    background: #eee;
    cursor: pointer;
    transition: background 0.2s;
  }
  
  .btn:hover {
    background: #ddd;
  }
  
  .operator {
    background: #f9a825;
    color: white;
  }
  
  .equal {
    grid-column: span 4;
    background: #43a047;
    color: white;
    font-weight: bold;
  }