Hello Ganesh Jagdale,
You can create custom theme for both Telerik and non-Telerik control. Non telerik controls won't work with application themes though. You will have to set a theme to theme through the StyleManager.Theme attached property. Check the attached project for example. It defines it's own class that extends telerik's Theme class, sets source to Generic.xaml and apply it to 2 buttons - one telerik and one non-telerik.
Thanks for your interest in our controls.
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