<% @Control Language="C#" %>
<script language="C#" runat="server">
    void btnSubmit_Click(Object Src, EventArgs E)
    {
        txtFeedback.Text = "Hello World!";
    }
</script>

<form runat=server>
    <asp:Button id="btnSubmit" text="Click" onclick="btnSubmit_Click" runat="server"/>
    <asp:Label id="txtFeedback" runat="server" />
</form>