Iris Docs: Dark theme ready

[tkknight]

🚀 Pull Request

Description

Updates the Iris docs to be dark theme ready. This is a feature that the pydata-sphinx-theme supports.

PR build of the docs: https://scitools-iris--5299.org.readthedocs.build/en/5299/index.html

Changes include

• Enabled the dark theme, this now adds an icons that toggles auto/dark/light (top right corner ish)
• svg images have an increased border to so when there is a dark background it looks better
• All images are transparent where appropriate
• datatables (used for the issue voting table)
  • Updated the datatables version (no visible changes here but I may have made the table dark mode friendly as it was not before hand)
  • Added some useful defaults for the table presentation
• Updated the dropdown syntax when using the code icon
• Specific a dark-light class where the figure/image is transparent, otherwise the theme will add a white background to the transparent image when using dark more. Sometimes this is ok though so the class has not been used everywhere.

Minor issue outstanding

The Iris Voted Issues table looks ok apart from the pulldown and text entry that uses black text on the almost black background, making it very hard to read. This is not a major issue and unless there are objections should not stop this PR.

I expect this issue will resolve itself when pydata-sphinx-theme is updated (and we unpin it) or when the datatables css is updated.

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Consult Iris pull request check list

[tkknight]

Will resolve #4795

[codecov]

Codecov Report

Patch and project coverage have no change.

Comparison is base (95cdea3) 89.35% compared to head (07e9b8b) 89.35%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5299   +/-   ##
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  Coverage   89.35%   89.35%           
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  Files          89       89           
  Lines       22417    22417           
  Branches     5382     5382           
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  Hits        20030    20030           
  Misses       1639     1639           
  Partials      748      748           

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[tkknight]

Ready for review.

[trexfeathers]

Thanks @tkknight. At least one fix to an image is needed, plus a few other comments.

[trexfeathers]

Great, thanks @tkknight! Let's save some monitor energy and some retinas 💻👁 ...