dark mode

[Fil]

See issue #408; here are things we learned doing dark-mode charts:

• use currentColor for black
• use a named variable for white
• if you use mixBlendMode: "multiply" (or "difference" or whatever) to mitigate occlusion, add a global isolation: isolate style to the plot, to avoid blending with the background.

we can use this discussion to add more remarks, and maybe how to make it simpler, for example, adding isolation: isolate to the default styles, or finding the best way to declare a stroke or fill as the "opposite of currentColor".

Transforming "white" to "black" with pure CSS: :root.dark marker[stroke=white] {stroke: "black");}

#1463
https://twitter.com/mbostock/status/1653069773645938689