Option 1:
The overlay scrollbars should be tight to the theme, so that a theme designed for users which visual impairment can easily opt out.
Best thing might be to have an opt-in policy where Ambiance and Radiance will explicitly say they want to use the overlay scrollbars.
Option 2:
Add an option in System Settings>Universal Access>Seeing to not to use them.
Option 1:
The overlay scrollbars should be tight to the theme, so that a theme designed for users which visual impairment can easily opt out.
Best thing might be to have an opt-in policy where Ambiance and Radiance will explicitly say they want to use the overlay scrollbars.
Option 2:
Add an option in System Settings>Universal Access>Seeing to not to use them.