Make dark scroll bar in dark theme

[rakleed]

@tvinzz @maximtop @kaprielov please take a look.

[kaprielov]

@rakleed Sorry for the late reply. You don't have to add color-scheme to media. Just add color-scheme: light dark; to :root or html.

[rakleed]

@kaprielov done.

[kaprielov]

I don't think vars.pcss is a good place to store it. common.pcss is better

[rakleed]

@kaprielov done.

[kaprielov]

Accept changes aa90becc55b