Dark mode for code snippets

[polytypic]

Code snippets in odoc HTML output are poorly readable (IMHO) in dark mode.

Here is a code snippet in dark mode:

Here is the same snippet in light mode:

Aside from the background and main foreground color the highlight colors appear to be unchanged and seem to be designed for light mode.

[Julow]

@EmileTrotignon has improved the code blocks themes in #1023
What do you think ?

[polytypic]

I assume the PR changes to the color scheme in this message. That looks much improved to me! 👍

Hmm... I think I personally might like a little bit higher contrast in the dark mode (especially for keywords — and I guess the low resolution of the screenshots might make the text seem less clear), but overall the improvement is substantial and I'd rather have the new scheme from the PR than wait for a perfect bikeshed color. :D

[EmileTrotignon]

I'd rather have the new scheme from the PR than wait for a perfect bikeshed color. :D

And the change also comes with a nice refactoring to the ways the color work, that should hopefully make it much easier to make more changes in the future.

[Julow]

Low contrasts are a problem but I think it's not caused #1023 as it uses the previous colors for documentation. Thanks for having a look :)