Straight to your question.
If you won't need any of our Alert Windows you can create a custom style and that will apply it for all Alert Windows in your application. Attached you will find a simple project which illustrates that. If you remove the x:Key
from the style and move the style in the application resources, that will apply it for all Alert Windows. But if you want to have different styles for each window you will have to keep the x:Key
and add 2 methods which will apply the style. You can see all that made in the sample project attached to that post.
If you have further questions please feel free to contact us again.
the Telerik team