body {
    font-family: 'Vazir', sans-serif;
    background: #1e1e1e;
    color: #fff;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    transition: background 0.3s, color 0.3s;
  }
  
  .calculator {
    background: #2c2c2c;
    padding: 20px;
    border-radius: 15px;
    box-shadow: 0 0 15px rgba(0,0,0,0.5);
    width: 320px;
    text-align: center;
  }
  
  h1 {
    margin-bottom: 15px;
  }
  
  #display {
    width: 100%;
    height: 50px;
    font-size: 20px;
    text-align: right;
    margin-bottom: 15px;
    padding: 5px 10px;
    border: none;
    border-radius: 8px;
    background: #444;
    color: #fff;
  }
  
  .buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 8px;
  }
  
  button {
    padding: 15px;
    font-size: 18px;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    transition: background 0.2s, transform 0.1s;
  }
  
  .btn {
    background: #555;
    color: white;
  }
  
  .operator {
    background: #007bff;
  }
  
  #equals {
    background: #28a745;
    grid-column: span 1;
  }
  
  #clear {
    background: #dc3545;
  }
  
  #themeToggle {
    background: #ffc107;
    color: black;
  }
  
  button:hover {
    transform: scale(1.05);
  }
  
  /* حالت روشن */
  .light {
    background: #f5f5f5;
    color: #222;
  }
  
  .light .calculator {
    background: #fff;
    color: #222;
  }
  
  .light #display {
    background: #e0e0e0;
    color: #000;
  }
  
  .light .btn {
    background: #ddd;
    color: #000;
  }
  
  .light .operator {
    background: #007bff;
    color: #fff;
  }
  
  .light #equals {
    background: #28a745;
  }
  
  .light #clear {
    background: #dc3545;
  }
  
  .light #themeToggle {
    background: #ffc107;
    color: black;
  }