Syntax highlighting on readthedocs.io of sphinx code-block

Question

I'm using RTD + Sphinx for my project ( redgrease = https://github.com/lyngon/redgrease ) and it seems like the syntax highlighting of code-blocks isn't working on the readthedocs.io page.

It only displays black text in a box.

E.g. see list item 3 at: https://redgrease.readthedocs.io/en/latest/intro.html#intro-redgrease

The syntax highlighting works fine when I build locally (with sphinx-build) as well as in VS Code using the reStructuredText plugin.

Working (local)

Not working (readthedocs.io)

The code blocks are all indented (as they appear inside lists), similar to this:

#. :ref:`Server-side Redis commands <red_commands>`.

    Allowing for ... blah blah ...
    It is ... yada yada ...

    .. code-block:: python
        :emphasize-lines: 8, 11, 13

        import redgrease
        import redgrease.utils

        # ... moar codes ..

What might be going on? Do i need some extension or add some config option? I don't have much trickery going on in the 'conf.py' nor '.readthedocs.yml'. (see repo)

Answer 1

The reason was painfully simple.

I had by mistake pinned a really old version of 'sphinx-rtd-theme' in my 'requirements.txt' file.

I had pinned version 0.1.5 instead of the latest 0.5.1
My local env simply had a more recent version.

Doh!