Add the controls in an asp panel
<asp:Panel ID="panel1" runat="server">
<asp:TextBox runat="server" ID="txt1" />
<input type="text" runat="server" id="txt2" />
</asp:Panel>
find the control and cast it
var txt1 = panel1.FindControl("txt1") as TextBox;
txt1.Style.Add("background-color", "orange");
var txt2 = panel1.FindControl("txt2") as HtmlInputText;
txt2.Style.Add("background-color", "blue");