I have create a Window with Ribbons (2010 – Microsoft.Windows.Controls.Ribbon).
It looks like that:

Now, is there a border over the tabs (between the tabs and the title). This is very ugly.
It should looks like Microsoft Office Word:

What can I do, that there is no border between the tabs and the titlebar?
(The RibbonWindow is used)
I use now the Fluent Ribbon, that solve the problem.