Thank you for contacting us.
To achieve your goal you will have to use a custom theme for the Docking. Please find the attached file in which a custom theme to the Docking is applied. Please mind for the "NOTE:"
comment which point the place where change have to be made.
If you need further assistance please let us know.
the Telerik team
Do you want to have your say when we set our development plans? Do you want to know when a feature you care about is added or when a bug fixed? Explore the Telerik Public Issue Tracking
system and vote to affect the priority of the items.