How to customize tittle bar of QMdiSubWindow with QStyleOptionTitleBar?

[marceloarguello700]

Hi i in my program have a QMdiarea, when the user
clik on new file, a QMdiSubWindow is added.

Inside the QMdiSubWindow is a Qmainwindow because need another menu an Qtoolbar

So the question is
how can change the QMdiSubWindow tittle bar, Or the child Qmainwindow

I want one with a slim tittle and a little close button.
Also want to customize the color of border and tittle background.

I know that exist QStyleOptionTitleBar but dont find any sample.
and the sample
http://qt-project.org/doc/qt-5/qtwidgets-widgets-styles-example.html
only change interior apearence.
Greetings