Enable Themes in you Web Site

I recently had to implement Themes in a Web Site that I am working on and found out that the .net framework has made it very easy to implement. Here is how I did it :

In my default.aspx page on the OnPreInit method (overridden) I simply add this :

protected override void OnPreInit(EventArgs e)

    {

        base.OnPreInit(e);

        if (Session["ThemeName"] == null)

        {

            Session.Add("ThemeName", "Green");

            Page.Theme = ((string)Session["ThemeName"]);

        }

        else

        {

            Page.Theme = ((string)Session["ThemeName"]);

        }

    }

Then from anywhere on the page I simply call this :

if (Session["MyTheme"] == null)

        {

            Session.Add("ThemeName", "Black");

        }

        else

        {

            if (((string)Session["ThemeName"]) == "Green")

            {

                Session["ThemeName"] = "Black";

            }

            else

            {

                Session["ThemeName"] = "Green";

            }

        }

Hope this helps, 

 - Tim