Similar to the sidebars in PEP 7 and PEP 8, we can add coloured sidebars and text to the version change directives.

Dark theme

Light theme

Accessibility check

• We're not relying on the colour in the sidebar or text to convey meaning. The words remains as before.
• The text like "Changed in version x.y" is now in colour. The contrast ratio meets at least the WCAG AA guidelines (4.5), with all but one meeting AAA (7.0).
• In dark mode, the same colour is used for the sidebar and the text:
  • Green: 7.13 (AAA)
  • Yellow: 12.07 (AAA)
  • Red: 4.53 (AA)
• In light mode, the sidebar colour is the same as in dark mode. The text needs to be darker to be readable:
  • Green: 7.08 (AAA)
  • Orange: 7.11 (AAA)
  • Red: 7.09 (AAA)

versionremoved

I also pre-emptively applied the red styling for the versionremoved directive, which will be released in the next Sphinx 7.3.0 (sphinx-doc/sphinx#11905).

Comparison with other themes

This is similar to how the Awesome theme does it.

These themes also add a background colour:

• Sphinx Book Theme
• PyData Sphinx Theme
• Sphinx theme for Wagtail

And Nefertiti for Sphinx adds a coloured box around it.