New docs website has some accessibility issues

[amellnik]

I noticed that the text in the header is very difficult to read due to the low contrast and ran it through a basic a11y tester (axe devtools). Many of these may have also existed in the previous version.

There's two things which would be very easy to fix:

• A few elements with insufficient contrast
• Links are not distinguished except by color

Some other issues which are slightly more involved to fix:

• Deprecated aria roles stemming from sphinx (doc-biblioentry, doc-backlist)
• Search area includes a scroll wrap even when there's thing possible to scroll

[amellnik]

Some of this is likely addressed by #269.

[ZacBlanco]

@amellnik Can you provide a more specific report? We can work on some items before the next release, but currently the issue description is too vague to take any actions.

We can control some basic things like some colors on the theme, but there are probably others items which are issues on the base theme (sphinx-immaterial) that we don't have control over. They might be better suited as issues filed on the theme's repository: https://github.com/jbms/sphinx-immaterial/