How to set font family to whole application?

Hi guys,

I have added a custom font in my app and want to set it as the default font to the whole app.
Any suggestions on how to do this? I tried a lot, for example making a style in ResourceDictionary and target the Label control, but no result.
It works when I set it to individual controls on a page, but i want to implement it to the whole application. Please help!

Regards,
Khos