You can remove the OS chrome by handling the ToolWindowLoaded and setting the e.Window.UseOsNonClientArea to false. You can restyle the PaneToolWindow. Note, the default styles for PaneToolWindow that we include in the xamDockManager xaml included in the DefaultStyles just references/bases on the default styles we have for the base class - ToolWindow which is in the Windows assembly so if you want to create your own style it would be best to take one of those styles and use that as your starting point.