Problem with style QTableView (headers) using stylesheets

Hello.

I've tried to style QTableView and its headers.

I've tried it like it is described here.

This worked for the headers itself but not the parts in the top left, top right and bottom left corner, shown on the attached image.

How can I style this parts?

Thank you.

push......

push......

No one any ideas?

Is this impossible with Qt?