Hi,
It is not officialy supported. Try the following sample but can be UI issue (i cannot guaranty that it will work always)
<%@ 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></title>
<style type="text/css">
#WestPanel-xcollapsed .x-tool{
position:absolute;
bottom:0;
margin:3px;
}
</style>
</head>
<body>
<ext:ResourceManager runat="server" />
<ext:Window
ID="Window1"
runat="server"
Title="Simple Layout"
Icon="Application"
Width="600"
Height="350"
Border="false"
Layout="Border"
Collapsible="true"
Plain="true">
<Items>
<ext:Panel ID="WestPanel" runat="server" Width="175" Title="Navigation" Region="West" Collapsible="true">
<Listeners>
<AfterRender Handler="this.el.dom.removeChild(this.header.dom);this.el.dom.appendChild(this.header.dom);" />
</Listeners>
</ext:Panel>
<ext:Panel runat="server" Region="Center">
</ext:Panel>
</Items>
</ext:Window>
</body>
</html>