Description

Many themes have at least two options for their CSS: light and dark mode. Dark mode is a common feature to help reduce strain on the eyes. We should offer something like this in the sphinx-book-theme, perhaps as a toggle.

Dark modes can help people parse some content more easily, so this is partially an accessibility issue.
Maybe others (@pradyunsg ?) have experience w/ this too.

Here's a blog post that describes how dark modes can work w/ minimal CSS changes: https://prudhvirampey.com/blog/colours/jekyll/css/fastpages/2020/10/30/hello-dark-mode.html

Another option would be to fix this in the pydata theme (in fact, @bollwyvl already has a shot at implementation). This would solve the problem for both themes! Here's a link to the issue: pydata/pydata-sphinx-theme#458

Actions

Here are the actions needed to do this:

• pydata theme release is made: https://github.com/pydata/pydata-sphinx-theme/releases/tag/v0.9.0
• update the dependency in the book theme
• Update pydata theme to 0.10 #597
• MAINT: Remove duplication with pydata-sphinx-theme #640
• Add support for a dark mode button
• Confirm there are no extra places to update our CSS for dark mode
• merge that in here and make a release of the book theme