* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
  }
  
  body {
    background-color: #f4f4f4;
    font-family: 'Arial', sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
  }
  
  .calculator {
    background-color: #fff;
    border-radius: 20px;
    box-shadow: 0 10px 20px rgba(0, 0, 0, 0.1);
    padding: 20px;
    width: 320px;
  }
  
  .display {
    margin-bottom: 20px;
  }
  
  #display {
    width: 100%;
    height: 60px;
    font-size: 2.5rem;
    text-align: right;
    padding: 10px;
    border: none;
    border-radius: 10px;
    background-color: #f1f1f1;
  }
  
  .buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
  }
  
  button {
    padding: 20px;
    font-size: 1.5rem;
    border: none;
    border-radius: 10px;
    background-color: #f1f1f1;
    cursor: pointer;
    transition: background-color 0.2s ease;
  }
  
  button:hover {
    background-color: #ddd;
  }
  
  button.operator {
    background-color: #ff8c00;
    color: white;
  }
  
  button.operator:hover {
    background-color: #e07b00;
  }
  
  button.clear {
    background-color: #ff0000;
    color: white;
  }
  
  button.clear:hover {
    background-color: #e00000;
  }