Hi,
Please look at the example.
Example
<%@ Page Language="C#" %>
<%@ Register Assembly="Ext.Net" Namespace="Ext.Net" TagPrefix="ext" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Ext.Net Example</title>
</head>
<body>
<form runat="server">
<ext:ResourceManager runat="server" />
<ext:Viewport runat="server" Layout="border">
<Items>
<ext:GroupTabPanel runat="server" Region="Center" TabWidth="150">
<Groups>
<ext:GroupTab runat="server">
<Items>
<ext:Panel runat="server" Title="Green" BodyStyle="background-color: Green;" />
<ext:Panel runat="server" Title="Yellow" BodyStyle="background-color: Yellow;" />
</Items>
</ext:GroupTab>
<ext:GroupTab runat="server">
<Items>
<ext:Panel runat="server" Title="Red" BodyStyle="background-color: Red;" />
<ext:Panel runat="server" Title="Blue" BodyStyle="background-color: Blue;" />
</Items>
</ext:GroupTab>
</Groups>
</ext:GroupTabPanel>
</Items>
</ext:Viewport>
</form>
</body>
</html>