Darker background colors in dark mode for increased contrast.

[isoos]

Following further Lighthouse reports on not enough contrast in certain context, and also comparing the brightness and (de)saturation of these colors with other dark mode palettes.

• #1b1b1b -> #121317 (default background)
• #373737 -> #2f3034 (hover bg)
• #41424c -> #242b32 (inset, code highlight bg)

Before/after example for hover:

Before/after example for code highlight:

[isoos]

/cc @parlough

[jonasfj]

I don't have any strong feelings here, mostly I hope we can align with dart.dev plans @parlough ?

[parlough]

Thanks for working to improve the contrast here!

I'm not sure I love completely losing the saturation. I feel it makes the site seem a bit grey/yellow and not Dart related.

I think to maintain some saturation and further improve the contrast, we can go a bit darker. I imagine many developers would want a bit darker anyway.

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Playing around a bit with the same content, I found something around this combination works pretty well. What do you think?

Page background: #121317
Code block background: #242b32

Slightly lower saturation and/or increased lightness could work as well, particularly for the code block.

[isoos]

Updated the PR and its images with the darker colors @parlough suggested + experimented with a relevant hover background too. (also staging update ongoing).
PTAL.