export html table layout to pdf lose style applied to the html document

Hi I am exporting html to pdf and this work fine but the style applied to my html is missing on the pdf document.

This is the code I am using:
 protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            if (Request.QueryString["ID"] != null)
            {
                try
                {
                    _orderinfo.OrderId = Convert.ToString(Request["ID"]);
                    OrderId = Request["ID"].ToString();
                    DataSet ds = _orderinfo.getOrderDetailsById();
                    DateTime today = DateTime.Today;
                    foreach (DataRow dr in ds.Tables[0].Rows)
                    {
                        string OrderReport = string.Format("<table><tr><td style='width: 475px;'><span style='color: firebrick;font-weight: bold;'>Hello</span></td><td></td><td>INVOICE</td></tr>");
                        OrderReport += string.Format("<tr><td><span style='color: firebrick;font-weight: bold;'>MarketPlace</span></td><td></td><td>Invoice #..............</td></tr>");
                        OrderReport += string.Format("<tr style='height:50px;'><td>TO:</td><td>SHIP TO:</td><td></td></tr>");
                        OrderReport += string.Format("<tr><td>{0}</td><td>{1}</td><td></td></tr>", dr["UserName"], dr["UserName"]);
                        OrderReport += string.Format("<tr style='height:100px;'><td><span style='text-transform:uppercase;'>Comments </span></td><td></td><td></td></tr>");
                        OrderReport += string.Format("<tr style='height:10px;'><td></td><td></td><td></td></tr></table>");
                        OrderInvoice.Text += OrderReport;

                    }
                }
                catch (Exception ex)
                {
                    Response.Write(ex.ToString());
                }
            }
            
        }
 protected void ExportPDF_Onclick(object sender, EventArgs e)
    {
        try
            {
                
                Response.ContentType = "application/pdf";
                Response.AddHeader("content-disposition", "attachment;filename=OrderDetails.pdf");
                Response.Cache.SetCacheability(HttpCacheability.NoCache);
                StringWriter sw = new StringWriter();
                HtmlTextWriter tw = new HtmlTextWriter(sw);
                this.Page.RenderControl(tw);
                StringReader sr = new StringReader(sw.ToString());
                Document Orderpdf = new Document(PageSize.A4, 10f, 10f, 50f, 0.0f);
                HTMLWorker htmlparser = new HTMLWorker(Orderpdf);
                PdfWriter.GetInstance(Orderpdf, Response.OutputStream);
                Orderpdf.Open();
                htmlparser.Parse(sr);
                Orderpdf.Close();
                Response.Write(Orderpdf);

                Response.End();
            }
            catch (Exception ex)
            {
                Response.Write(ex.ToString());
            }
        
    }
Can some help telling me why the style is not applied to the pdf document.