I attatch a sample to reproduce the issue

you can see the issue on the lefttop of picture

Hello,

I can suggest you define your TestRibbon class like this:

public class TestRibbon : XamRibbon
{
    public TestRibbon()
    {
        this.SetResourceReference(StyleProperty, typeof(XamRibbon));
    }
}

Please let me know if this helps you or you need further assistance on this matter.

Looking forward for your reply.

It works fine. Thanks

Hello,

Thank you for your feedback. I am glad that you resolved your issue and I believe that other community members may benefit from this as well.

Thanks again.