Accessibility improvements to the left nav

[davidfischer]

This makes a few color changes to the left navigation with an eye toward improved accessibility. Specifically, I looked at the colors on our existing theme and they don't have enough contrast. The headings are the worst offenders but some of the links aren't fantastic.

Ping @mahmoud

[Blendify]

The improvements and code look good!
This also fixes #453

[jessetan]

Definitely an improvement.

The contrast between toctree captions like "Demo documents" and the links has decreased with these changes. Have you considered making the entire menu background a bit darker (versions menu bg could go to full black)? This will also increase contrast between bg and text, and you don't have to lighten the captions as much.

[davidfischer]

By itself though, going to jet black (#000) will not solve the problem. The accessibility rating would only be acceptable for large headings.

The other problem is that the left navigation would blend in with the version menu at the bottom ("Read the Docs v:latest")

I suspect we can slightly darken the captions ("Demo documents") though while still keeping a good rating. I'll see what I can do.

[davidfischer]

I made a slight tweak to the colors to try to get a little more differentiation between the captions ("DEMO DOCUMENTS") and the links ("Structural elements"). I reduced it down to essentially the least contrast of the caption so that we retain a AA accessibility rating with the background.

[mahmoud]

Excellent! Is there a milestone / timeline for getting this released? I assume I'll just have to re-pin to the new release in my requirements.txt.

Thanks!

[davidfischer]

If you've pinned to a precise version, yes, you'll need to re-pin.

If you haven't, or you pinned to something like sphinx-rtd-theme<0.4 (which will be the default after readthedocs/readthedocs.org#4096), then it should just happen automatically. I aim to get both of these changes out next week.