body {
      font-family: Arial, sans-serif;
      background: #f0f0f0;
      padding: 20px;
    }
    form, .invoice, .download-container {
      background: #fff;
      max-width: 900px;
      margin: auto;
      padding: 20px;
      border-radius: 12px;
      box-shadow: 0 0 10px rgba(0,0,0,0.1);
    }
    h2 {
      text-align: center;
    }
    input, select {
      padding: 8px;
      width: 100%;
      margin-bottom: 10px;
    }
    table {
      width: 100%;
      border-collapse: collapse;
      margin-top: 15px;
    }
    th, td {
      border: 1px solid #ddd;
      padding: 8px;
      text-align: center;
    }
    .btn {
      margin-top: 10px;
      padding: 10px 15px;
      background-color: #007bff;
      color: white;
      border: none;
      border-radius: 5px;
      cursor: pointer;
    }
    .btn-add { background-color: #28a745; }
    .btn-remove { background-color: #dc3545; }
    .invoice {
      display: none;
      margin-top: 30px;
    }
    .download-container {
      display: none;
      text-align: center;
      margin-top: 20px;
    }