G4P dropList changing roundcorners of scrollbar

I’m trying to change roundcorners and the border color of the scrollbar into a dropList.
Is there a way to do that ?
I’ve tryed to put g4p_controls.GButton.useRoundCorners(false), but it has no action on the scrollbar.
I’ve seen this old post from 2017 https://forum.processing.org/two/discussion/20223/g4p-custom-scrollbar-and-text-anti-aliasing
Do you have any idea ?

Thanks for your answer!

look here:
for the color schemes and on page 2:
for additional info about which color ges where.

As far as I know, 4 and 6 are the silder color when no mouse is over and when a mouse is over.

It is not possible to change the round-corners on the scrollbar.

Ok thank you for your answer!
Have a nice day