Iris Documentation: Needs to be dark mode friendly

[tkknight]

📚 Documentation

pydata-sphinx-theme has been updated from 0.8.1 to 0.9.0. The later version supports dark mode which is great, however the iris docs will need a few changes like image transparency, dark friendly logo, etc.

The biggest item to fix is the expandable panels colours are not associated with the theme (always white).

Suggest we:

• Pin to version 0.8.1 whilst we update the docs (pinned pydata-sphinx-theme until the docs are dark mode friendly. #4796)
• Fix the mentioned issues
• Unpin

[trexfeathers]

dark friendly logo

#3935

[rcomer]

Dark mode is already showing in the latest docs 😕

[tkknight]

I believe that is due to readthedocs (latest) using the main branch for the requirements, that use use the env definition https://github.com/SciTools/iris/blob/main/requirements/ci/readthedocs.yml (symlink to iris.yml -> py38.yml).

PR #4796 to pin to the non dark mode version has not been merged just yet. We have some CI issues atm so the PR will not pass - feel free to merge though, it is a minor change.

[trexfeathers]

• Also create a dark mode version of the banner logo. marketing#2