Thank you for writing.
The "Desert" theme, unlike the most other themes is not stored in the resources of the corresponding control DLLs. Instead, the xml files you need to use this theme can be found in the "Examples\Themes" folder of Q3 installation path. (For your convenience we are also attaching those files to this post)
The next step for you would be to add the files you need as resources to your application and use the ThemeManager
component to load them up. Here you can read more on loading external themes in your applications:
One of the main reasons for us to choose this distribution approach for the desert theme, is to minimize your applications's loading time and memory footprint.
If you have any additional questions, please do not hesitate to contact us.
All the best,
the Telerik team