Looks like that game is built on an almost 6 years old Ren'Py version, which is ancient compared to the modern Ren'Py and missing loads of features and apparently also all default Ren'Py styles that my patch was made to modify. Why the hell would anyone in the right mind still use this old software is beyond me.
Even if I would be able to find time to search through its configuration, It's highly unlikely that my patch would still work on such an old Ren'Py version and I have no intention to create a separate patch, that would work on long time outdated Ren'Py.
No chance, no way.
It would be easier to modify the game itself to remove the background and maybe add outlines to text.