Respect the stylix.polarity option and unset programs.regreet.extraCss
to enable custom styling.
This partially resolves the "ReGreet not using GTK or cursor theme" [1]
issue.
[1]: https://github.com/danth/stylix/issues/690
Link: https://github.com/danth/stylix/pull/723
Reviewed-by: NAHO <90870942+trueNAHO@users.noreply.github.com>