feature: UI needs dark mode support

[RoryBlyth]

Need color set for dark mode. Currently, it's off-white text on a white background.

[csells]

it doesn't need to auto-switch to dark mode but it should be able to be styled to look good in dark mode.

[csells]

perhaps we start with a set of default dark styles that's the inverse of the default light styles ala https://stackoverflow.com/a/66965199/185286

[csells]

this is what I got with a combo of inversion and some hand tweaking: