Feature/darkmode

[r-4bb1t]

I modified it so that it can be used if you give the html tag a darkmode classname. There may still be some shortcomings.

[sakofchit]

this is a good start! but it looks like it breaks a few things:

1. default buttons don't have the black border

2. selected dropdown menu isn't highlighted

3. Darkmode scrollbar arrow svgs don't seem to display

4. box shadows should probably have a white offset instead of black

[r-4bb1t]

I revised the contents you wrote, so I'd appreciate it if you could check it.