body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background: #f4f4f4;
    font-family: sans-serif;
    margin: 0;
  }
  
  .calculator {
    background: #222;
    padding: 20px;
    border-radius: 12px;
    box-shadow: 0 0 20px #00000055;
    width: 280px; 
  }
  
  #display {
    width: 100%;
    height: 60px;
    margin-bottom: 15px;
    font-size: 28px;
    text-align: right;
    padding: 10px 15px;
    border: none;
    border-radius: 10px;
    background-color: #333;
    color: #fff;
    box-sizing: border-box; 
    box-shadow: inset 0 0 8px #00000055;
  }
  
  
  .buttons {
    display: grid;
    grid-template-columns: repeat(4, 60px);
    gap: 10px;
  }
  button {
    height: 60px;
    font-size: 20px;
    border: none;
    border-radius: 6px;
    background: #444;
    color: #fff;
    cursor: pointer;
    transition: background 0.3s;
  }
  button:hover {
    background: #666;
  }