DOC: Syntax highlight not always working
Looks like something is wrong while rendering the documentation, regarding syntax highlighting of code blocks.

See for example: https://dev.pandas.io/docs/user_guide/reshaping.html#multiple-levels

The first block code has no colors, just black. The next block is coloring the `In[27]`, the literals.

Checking the markdown in `doc/source/user_guide/reshaping.rst` I can't see any obvious difference among them. But for some reason Sphinx just highlights one.

CC: @jorisvandenbossche not sure if this is related to the new theme, or was happening before