I am sorry if given information was puzzling or misleading for you.
Basically, yes, you would need to set the theme to each CheckBox in your applciation. To avoid doing that, you could have an implicit style in App.xaml that, as mentioned earlier, you can base on an existing Telerik theme.
So, for a CheckBox, for example, you can have in App.xaml:
And for all RadControls, the ApplicationTheme will be working well:
I hope this information will give you a solution.
the Telerik team
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