Border and background colour is not showing in pdf

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ASP.NET

Hello all,
I am generating a pdf using following code

HtmlForm form_html = new HtmlForm();
       form_html.Controls.Add(GridView1);
       string attachment = "attachment; filename=Article.pdf";
       Response.ClearContent();
       Response.AddHeader("content-disposition", attachment);
       Response.ContentType = "application/pdf";
       StringWriter stw = new StringWriter();
       HtmlTextWriter htextw = new HtmlTextWriter(stw);
       divtext.RenderControl(htextw);
       GridView1.RenderControl(htextw);
       Document document = new Document(PageSize.A4, 3f, 4f, 1f, 0f);
       PdfWriter.GetInstance(document, Response.OutputStream);
       document.Open();
       StringReader str = new StringReader(stw.ToString());
       HTMLWorker htmlworker = new HTMLWorker(document);
       htmlworker.Parse(str);
       document.Close();
       Response.Write(document);
       Response.End();

code works fine but it is not showing border and background color of