In WPF, how do I get the content of a tabItem to fill available space?

I do not know what I am doing wrong here. In the XAML below, the Border does not fill the available space on the tabItem (just lots of whitespace). How do I fill the entire tab page?

<TabControl>
    <TabItem Header="Plant State">
        <Border Background="Red" VerticalAlignment="Stretch" HorizontalAlignment="Stretch"></Border>
    </TabItem>
</TabControl>

From stackoverflow

• Nest a DockPanel in there, have you tried that?

  Andrew

  willem : Hi Andrew, I've tried adding a dockPanel and a Grid, but neither of them make a difference.

• I figured this out with the help of Matt Hamilton. This actually works fine if you are using a regular TabControl (default Template).

  I am using a xaml "theme" that alters the default control template. That is causing the layout to fail, so I will have to investigate and figure out what is wrong.

  Nelson Reis : Have you found how to solve this problem? I'm having the same issue...

• Can you post the answer when you find out what is wrong ? I am having the same issue when I use 'theme'