How to Fix Header and Sub-Header in Repeater in ASP.NET - css

Question

How to fix header and sub-Header when scroll-up or down of Repeater i am trying with CSS (style) Ref. link(https://www.aspdotnet-suresh.com/2015/03/aspnet-scrollable-repeater-control-with-fixed-column-header-using-css-in-csharp-vbnet.html) and that is work properly for single header but not for sub-header, is there any way to do this?
Repeater
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.1.1/jquery.min.js"></script>
<script>
$(document).ready(function () {
$("table").prepend("<tr style=' color: white; background-color: #9494b9;'> <th>Column 1</th><th colspan='2'>Column 2</th><th colspan='2'>Column 3</th></tr>")
})
</script>
<style type="text/css">
#rpttable tr td
{
max-height:10%;
}
table {
border-collapse: collapse;
text-align: center;
}
</style>
<asp:Repeater ID="rptDrugs" runat="server" >
<HeaderTemplate>
<table border="1" id="rpttable">
<tr style=" color: white; background-color: #9494b9;">
<th scope="col" style="width: 80px"> </th>
<th scope="col" style="width: 80px">Dosage
</th>
<th scope="col" style="width: 120px">Drug
</th>
<th scope="col" style="width: 100px">Patient
</th>
<th scope="col" style="width: 100px">Date
</th>
</tr>
</HeaderTemplate>
<ItemTemplate>
<tr>
<td>
<asp:Label ID="Label2" runat="server" Text="" />
</td>
<td>
<asp:Label ID="lblCustomerId" runat="server" Text='<%# Eval("Dosage") %>' />
</td>
<td>
<asp:Label ID="lblContactName" runat="server" Text='<%# Eval("Drug") %>' />
</td>
<td>
<asp:Label ID="lblCountry" runat="server" Text='<%# Eval("Patient") %>' />
</td>
<td>
<asp:Label ID="Label1" runat="server" Text='<%# Eval("Date") %>' />
</td>
</tr>
</ItemTemplate>
<FooterTemplate>
</table>
</FooterTemplate>
</asp:Repeater>
CS
protected void Page_Load(object sender, EventArgs e)
{
DataTable table = new DataTable();
table.Columns.Add("Dosage", typeof(int));
table.Columns.Add("Drug", typeof(string));
table.Columns.Add("Patient", typeof(string));
table.Columns.Add("Date", typeof(DateTime));
// Here we add five DataRows.
table.Rows.Add(25, "Indocin", "David", DateTime.Now);
table.Rows.Add(50, "Enebrel", "Sam", DateTime.Now);
table.Rows.Add(10, "Hydralazine", "Christoff", DateTime.Now);
table.Rows.Add(21, "Combivent", "Janet", DateTime.Now);
table.Rows.Add(100, "Dilantin", "Melanie", DateTime.Now);
rptDrugs.DataSource = table;
rptDrugs.DataBind();
}