Don't override Pygments background color in code cells

[mgeier]

See #447.

I'm very unsure if that's actually a good idea.

Interestingly, most themes force their own background color, so this would only work with a subset of themes (e.g. with the RTD theme).

Apart from this, I'm hesitating because many people use the Pygments style 'sphinx' (because it's the one used by sphinx-quickstart), which has a quite ugly green background.
If we were to merge this PR, many people would suddenly get a green background on their code cells (which they probably don't want).

Any comments/suggestions?

[mgeier]

Good news everyone: sphinx-quickstart doesn't use the style 'sphinx' anymore, see sphinx-doc/sphinx#5282 and sphinx-doc/sphinx#5700.

This makes it less of a problem for new users, but people using an old conf.py might still be surprised when their code cells suddenly turn green.

[mgeier]

Of all the (about 30) themes mentioned in https://nbsphinx.readthedocs.io/usage.html#HTML-Themes, the Pygments background seems to be only visible on those:

• bizstyle
• dask_sphinx_theme
• sphinx_material
• sphinx_rtd_theme
• traditional

I'm not sure whether that's a relevant argument for or against this PR, but I think it is remarkable anyway. I find it interesting that not even all the built-in themes respect the Pygments background.

Note that in the julia theme the syntax highlighting doesn't seem to work at all, and in the sphinx_typlog_theme, the Pygments style seems to be forced (and the pygments_style setting seems to be ignored).

[mgeier]

In the bootstrap-astropy theme, the Pygments background is only visible in the very corners (see the black corners):

This is a hint that the CSS still isn't quite right.
Any ideas how to fix this?

[DominiqueMakowski]

About the yellow background argument, yes some users might be surprised, although it is ultimately quite a specific issue to search for and easy to fix. A side effect is that these users will automatically be "notified" of the new possibility of further customizing the look of their converted notebooks ☺️

About the CSS issue, really sorry but that's completely out of my range! I send some positive vibes tho 🤞

[mgeier]

I've created PRs to fix the built-in themes (sphinx-doc/sphinx#7718, sphinx-doc/sphinx#7721) and in the alabaster theme (sphinx-doc/alabaster#169).