Delete this (above mentioned) section.. You have just removed the "gap"
Now this will work if you do not set the header (as you have shown in example). However if you set the header, it'll go behind the border. So to correct this, just set Panel.ZIndex="-1" in the border that was enclosing the section you just deleted (it looks like <Border BorderBrush="White" BorderThickness= ...)
(2) Use duplicate GroupBox and flip it horizontally and place it beneath original groupbox:
Put this code below your groupbox (assuming your groupbox's name is 'OriginalGroupbox')
Best Answer
No such standard control, but it it is easy to create your own. Here is a sample implementation:
And the accompanying css for it:
The code is from a example I created in response to an Oracle JavaFX forum thread post "Equivalent to BorderFactory.createTitledBorder".
The output of the example program is as shown below.