I am looking for an option name or way how to remove some kind of border around user control which I used for task pane. It is standard empty UserControl. As you can see in the first picture, there is task pane with user control without border. In the second picture there is another task pane but with border. It is about 2-3 pixels wide. I have created both task pane. The first one was created couple of months ago, maybe a year ago. I do not remember how I did it. It is very frustrating for me. I spent some hours to find a way how I did it but without success.
I compared also UserControl.Designer.cs files, but no difference. I mean UserControls files between those two task panes.
To be more specific, here are some properties which are currently set and do not help.
Margin = 0
Padding = 0
BorderStyle = None
Could someone give me correct direction how to solve it, please?