ListView - Scrollable With Fixed Headers Using CSS

I am using an ASP.NET ListView control and, at the moment, I have a scrollable grid: (example below is simplified and contains embedded styling for sake of question)

<asp:ListView ID="ListView" runat="server" DataKeyNames="Id">
<LayoutTemplate>
<div style="height:225px; overflow:auto;">
<table runat="server">
<tr>
<th>
<span>Column1</span>
</th>
<th>
<span>Column2</span>
</th>
<th>
<span>Column3</span>
</th>
</tr>
<tr id="itemPlaceholder" runat="server" />
</table>
</div>
</LayoutTemplate>
<ItemTemplate>
<tr id="items" runat="server">
<td class="first">
<%#Eval("Column1")%>
</td>
<td>
<%#Eval("Column2")%>
</td>
<td>
<%#Eval("Column3")%>
</td>
</tr>
</ItemTemplate>
</asp:ListView>

I'd like to apply CSS such that my headers are fixed. What styling can I add to make it work?