Thank you for your help, I think we're getting in the right direction!
However, I could not completely understand where you were heading at.
I have generated a style for the RadPaneGroup that contains the RadDocumentPane.
Then, I should find the ContentControl... how do I do that?
I work with Visual Studio, not Blend. So what I've got is this:
I have tried to add a Property = Template and have that Template Target at 'ContentControl'. But that is - as I assumed - a shot in the dark. I assume that there can (and will) be multiple contents inside the RadPaneGroup that inherit from ContentControl. I ran it and it doesn't give any change in the looks.
I started Blend for a split second and tried it there too, but no luck. I first had to rewire the references to the controls, but I think that's obvious. First, I cannot see the DocumentPane in my Object tree. In the Design view, I cannot select it; Blend only lets me select the parent around it. I put my cursor on it in code and yes, I got properties for it. I can see there's a style set for it... but then. My lacking knowledge of Blend may contribute to this :)
I'm getting somewhere, but at this point, stuck again. Could you help me some more?