css missing in converted pdf using c#

 public enum ExportTypes
 {
   Excel, PDF, TextFile
 }

 public class ExportManager
 {
   public static bool Downloader(GridViewReport grdReport, ExportTypes type)
   {
      HttpContext.Current.Response.ClearContent();
      StringWriter sw = new StringWriter();
      HtmlTextWriter htw = new HtmlTextWriter(sw);
      string selectedType = string.Empty;
      switch (type)
      {
        case ExportTypes.Excel:
          selectedType = "xls";
          grdReport.ExportType = ExportTypes.Excel;
          grdReport.FileName = grdReport.FileName + ".xls";
          grdReport.RenderControl(htw);
          HttpContext.Current.Response.Write(grdReport.ReportHeader + 
          sw.ToString());
          break;
        case ExportTypes.PDF:
          selectedType = "pdf";
          grdReport.RenderControl(htw);
          HttpContext.Current.Response.ContentType = "application/pdf";
          string fileName2Save = grdReport.FileName.Replace(" ", "").
          Replace("/", "-") + ".pdf";
          HttpContext.Current.Response.AddHeader("content-disposition", 
          "attachment; filename=" + fileName2Save);
          HttpContext.Current.Response.Cache.
          SetCacheability(HttpCacheability.NoCache);
          break;              
      }
      if (selectedType == "pdf")
      {
         HttpContext.Current.Response.Cache.SetCacheability(HttpCacheability.
         NoCache);
         StringReader sr = new StringReader(grdReport.
         ReportHeader + "\r\n" + sw.ToString());
         Document pdfDoc = new Document(PageSize.A4, 10f, 10f, 10f, 4f);
         HTMLWorker htmlparser = new HTMLWorker(pdfDoc);
         PdfWriter.GetInstance(pdfDoc,HttpContext.Current.Response.OutputStream);
         pdfDoc.Open();
         //pdfDoc.HtmlStyleClass = BaseFont.TIMES_ROMAN;  // "clsReportStyle";
         htmlparser.Parse(sr);
         pdfDoc.Close();
         HttpContext.Current.Response.Write(pdfDoc);
         HttpContext.Current.Response.Flush();
         HttpContext.Current.Response.End();
      }
      else
      {
         HttpContext.Current.Response.ContentType = 
         grdReport.ExportType.ToString();
         HttpContext.Current.Response.AddHeader("content-disposition", 
         "attachment;filename=" + grdReport.FileName);
         grdReport.Dispose();
         HttpContext.Current.Response.End();
      }
      return true;
  }
}

public class GridViewReport : GridView
{
   public string ReportHeader { get; set; }
   public string FileName { get; set; }
   public ExportTypes ExportType { get; set; }

   public GridViewReport()
   {
       RowStyle.VerticalAlign = VerticalAlign.Top;
       CssClass = "clsReportStyle";  // Here is the Css were defined...
   }      
}