body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background: #f4f4f9;
    font-family: Arial, sans-serif;
  }
  
  .calculator {
    background: #fff;
    padding: 20px;
    border-radius: 15px;
    box-shadow: 0px 4px 10px rgba(0,0,0,0.1);
    width: 260px;
  }
  
  #display {
    width: 100%;
    height: 50px;
    font-size: 1.5em;
    text-align: right;
    margin-bottom: 10px;
    padding: 2px;
    border-radius: 8px;
    border: 1px solid #ddd;
    outline: none;
  }
  
  .buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
  }
  
  .btn {
    padding: 20px;
    font-size: 1.2em;
    border: none;
    border-radius: 8px;
    background: #eaeaea;
    cursor: pointer;
    transition: 0.2s;
  }
  
  .btn:hover {
    background: #d4d4d4;
  }
  
  .equal {
    grid-column: span 2;
    background: #4CAF50;
    color: white;
  }
  
  .equal:hover {
    background: #45a049;
  }