body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
    background: #f0f0f0;
    font-family: Arial, sans-serif;
  }
  
  .calculator {
    width: 300px;
    background: #ffffff;
    border-radius: 10px;
    box-shadow: 0 4px 10px rgba(0, 0, 0, 0.2);
    overflow: hidden;
  }
  
  .display {
    background: #222;
    color: #0f0;
    font-size: 2rem;
    padding: 20px;
    text-align: right;
    border-bottom: 2px solid #ccc;
    height: 60px;
  }
  
  .buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    padding: 10px;
  }
  
  button {
    font-size: 1.2rem;
    padding: 15px;
    background: #007bff;
    color: #fff;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    transition: 0.3s;
  }
  
  button:hover {
    background: #0056b3;
  }
  
  button:active {
    background: #003f7f;
  }