How to make the selected TabItem look attached to the rest of the document

I have a WPF app with a few Tabs. I'm now messing around with styling and have for example changed the ControlTemplate so I now have to define everything about the TabItem.

Now the TabItem that is selected seems detached from the document below because of some thin line around that content (there is no border). I'm not sure w开发者_如何转开发hat technique to use to make it look attached again.

My guess would be that the Header-template is responsible for the problem. You can style that too tho - see this example for details: http://www.switchonthecode.com/tutorials/the-wpf-tab-control-inside-and-out