Fix codebgcolor and codetextcolor for Sphinx 3.1.0+

[zmwangx]

Sphinx 3.1.0+ dropped the custom codebgcolor and codetextcolor from the classic theme (see commit sphinx-doc/sphinx@b345acc), leaving pre elements uncolored.

Without the fix:

Should be:

[zmwangx]

Wait, was this change intentional? Just noticed that Python 3.10 docs, rendered with Sphinx 3.2.1, features background color-less code blocks.

In any case I certainly prefer the old style.

[JulienPalard]

Looks related to sphinx-doc/sphinx#7720 / sphinx-doc/sphinx#7721

[zmwangx]

Yeah, sphinx-doc/sphinx#7720 led to sphinx-doc/sphinx#7721 led to sphinx-doc/sphinx@b345acc.

[corona10]

https://bugs.python.org/issue42042

[pablogsal]

@Mariatta Do you happen to know who has privileges to publish a new version to pypi? We need a new version to restore the colourized backgrounds.

[Mariatta]

I can publish this later this evening.

[Mariatta]

We've released v 2020.12
On PyPI: https://pypi.org/project/python-docs-theme/2020.12/
Changelog https://github.com/python/python-docs-theme/releases/tag/v2020.12

[pablogsal]

Thanks a lot @Mariatta!