Hello

 I just want to know which code determines that which stylesheet is picked up.

App_Themes/Blue

App_Themes/Green

App_Themes/Red

Regards,

Sai 

In OnPreInit, you can switch the theme by setting the Page.Theme property to a value.  Normally you can set the Theme in the @Page directive in the ASPX markup, but you can change the theme in OnPreInit, and assign it a value like this.Page.Theme = "Blue";

Along with the above, I do not wish to change themes, so I just set one as the default.
That is done in your web.config file.

Thanks. I got it.