Export HTML string to Excel with formatting in ASP.Net

Refer this

HTML

<asp:Button Text="Export To Excel" OnClick="ExportToExcel" runat="server" />

Namespaces

using System.Data;
using System.Text;

C#

protected void ExportToExcel(object sender, EventArgs e)
{
    DataTable dt = new DataTable();
    dt.Columns.AddRange(new DataColumn[3] {
    new DataColumn("Id"),
    new DataColumn("Name"),
    new DataColumn("Country")});
    dt.Rows.Add(1, "John Hammond", "United States");
    dt.Rows.Add(2, "Mudassar Khan", "India");
    dt.Rows.Add(3, "Suzanne Mathews", "France");
    dt.Rows.Add(4, "Robert Schidner", "Russia");

    StringBuilder sb = new StringBuilder();
    sb.Append("<table width='100%' cellspacing='0' cellpadding='2'>");
    sb.Append("<tr><td align='center' style='background-color: #18B5F0' colspan = '2'><b>Order Sheet</b></td></tr>");
    sb.Append("<tr><td colspan = '2'></td></tr>");
    sb.Append("<tr><td><b>Order No:</b> 100</td><td><b>Date: </b>" + DateTime.Now + " </td></tr>");
    sb.Append("<tr><td><b>From :</b> " + "Company Name" + " </td><td><b>To: </b>" + " Some Company " + " </td></tr>");
    sb.Append("</table>");

    sb.Append("<table border = '1'>");
    sb.Append("<tr>");
    foreach (DataColumn column in dt.Columns)
    {
        sb.Append("<th style = 'background-color: #D20B0C;color:#ffffff'>");
        sb.Append(column.ColumnName);
        sb.Append("</th>");
    }
    sb.Append("</tr>");
    foreach (DataRow row in dt.Rows)
    {
        sb.Append("<tr>");
        foreach (DataColumn column in dt.Columns)
        {
            sb.Append("<td>");
            sb.Append(row[column]);
            sb.Append("</td>");
        }
        sb.Append("</tr>");
    }
    sb.Append("</table>");
    Response.Clear();
    Response.Buffer = true;
    Response.AddHeader("content-disposition", "attachment;filename=ReceiptExport.xls");
    Response.Charset = "";
    Response.ContentType = "application/vnd.ms-excel";
    string style = @"<style> .textmode { } </style>";
    Response.Write(style);
    Response.Output.Write(sb.ToString());
    Response.Flush();
    Response.End();
}

Screenshot