RadOpen RenderMode and Skins

Thanks marin, but I have tried successfully to skin but rendermode still does not work, I use radwindow within radwindow, this is my source:

 web.config:

 <appSettings>
    <add key="Telerik.Skin" value="Vista"/>
    <add key="Telerik.Window.Skin" value="WebBlue" />
    <add key="Telerik.Web.UI.Window.RenderMode" value="lightweight" />
    <add key="Telerik.EnableEmbeddedSkins" value="true" />
    <add key="Telerik.EnableEmbeddedBaseStylesheet" value="true"/>
    <add key="Telerik.ScriptManager.TelerikCdn" value="Disabled"/>
    <add key="Telerik.StyleSheetManager.TelerikCdn" value="Disabled"/>
  </appSettings>
 
popup.aspx:

        <form id="popup" runat="server" style="background-color:silver;width:674px; height: 632px;">
              <asp:Button runat="server" id="case_solution" Text="Add Case/Solution"  OnClick="case_solution_Click" Font-Names="Arial" Font-Size="8pt" />

        <telerik:RadScriptManager ID="RadScriptManager1" runat="server">
        <Scripts>
            <asp:ScriptReference Assembly="Telerik.Web.UI" Name="Telerik.Web.UI.Common.Core.js" />
            <asp:ScriptReference Assembly="Telerik.Web.UI" Name="Telerik.Web.UI.Common.jQuery.js" />
            <asp:ScriptReference Assembly="Telerik.Web.UI" Name="Telerik.Web.UI.Common.jQueryInclude.js" />
        </Scripts>
    </telerik:RadScriptManager>
    <script type="text/javascript">
        function GetRadWindow() {
            var oWindow = null;
            if (window.radWindow)
                oWindow = window.radWindow; else if (window.frameElement.radWindow)
                    oWindow = window.frameElement.radWindow; return oWindow;
        }

        function radwindowpop(url) {
           var oBrowserWnd = GetRadWindow().BrowserWindow;
            var parentRadWindowManager = oBrowserWnd.GetRadWindowManager();
     
            //parentRadWindowManager.set_reloadOnShow(true);
            parentRadWindowManager.setSize(534, 410);
            parentRadWindowManager.set_behaviors(Telerik.Web.UI.WindowBehaviors.Move + Telerik.Web.UI.WindowBehaviors.Close);
            parentRadWindowManager.set_title("<b>CASE and Solution</b>");
            parentRadWindowManager.set_visibleStatusbar(false);
            parentRadWindowManager.set_overlay(true);
            parentRadWindowManager.set_enableShadow(false);
            parentRadWindowManager.set_visibleTitlebar(true);
            parentRadWindowManager.set_autoSize(false);
            parentRadWindowManager.set_modal(true);
 
            var newWin = parentRadWindowManager.open(url, "RadWindow1");
            newWin.firstDialogReference = GetRadWindow();
            
            newWin.setActive(true);
            
        }
        //Put your JavaScript code here.
    </script>
    <telerik:RadAjaxManager ID="RadAjaxManager1" runat="server">
    </telerik:RadAjaxManager>
    <telerik:RadWindowManager ID="RadWindowManager1" runat="server" EnableEmbeddedSkins="true" Skin="Vista" Height="63px">
        <Windows>
            <telerik:RadWindow ID="RadWindow1" runat="server" Skin="Metro" RenderMode="Lightweight" Title="Black skin"></telerik:RadWindow>
        </Windows>
    </telerik:RadWindowManager>
     </form>

popup.aspx.cs:

                 ClientScript.RegisterStartupScript(this.GetType(), "openpopup2", "radwindowpop('www.google.com');", true);