I'm doing some UI customisation with themes. One of the things I'm changing is the File Dialog box. I've found the color and font for the title but not the property to change the background color/opacity. It defaults to completely transparent, as the screenshot shows.


The files area is themed by a Tree class, the buttons by a Button, but I can't figure what controls the title opacity. It should be near the color and font, I think.
Anyone can help? Thank you.