Fix doxygen-awesome dark mode

[hidmic]

Precisely what the title says. CSS scoping for html elements was leaving a fair amount of rules behind, such as those for html.dark-mode elements. Also, some light theme appropriate coloring was tagged as !important. This patch fixes it all.

[twodrops]

@hidmic Thanks a lot for the PR :) Which theme did you test it with?
I tested it with the pydata theme used in this repo for demo and the changes seems to have impacted the light mode.

@aniketsalve22 Could you please test it with pydata theme used in the demo, rtd-theme and book-theme?

[hidmic]

Which theme did you test it with?

I'm using the sphinx-book-theme but without many of the customizations you have in this repo.

[twodrops]

Alright. @aniketsalve22 I guess it then makes sense to test the changes without any of our customisations.
Also @Maetveis has achieved cool customisations here from which we can draw some inspiration.

[hidmic]

AMD docs look pretty too. Don't mind which path we take so long as we can get the dark mode to work.

Great tool BTW.

[twodrops]

@aniketsalve22 Just realized we are using sphinx-book-theme for demo as well and not pydata-theme.

[Maetveis]

I mentioned on #100 that I can with upstreaming my changes, I don't have the time right now, but I can give a brief summary of what I did for the ROCm documentation:

For ROCm documentation the style is applied by a the "rocm-docs" sphinx theme hosted here: https://github.com/ROCm/rocm-docs-core. It is in turn based on sphinx-book-theme.

The PR that added the styling you see was ROCm/rocm-docs-core#36.

The source of extra_stylsheet is doxygen_awesome.css scoped to the doxygen-content class similarly of what doxysphinx does dynamically with sass. To avoid the node dependency, which would have been painful for the many ROCm projects, I instead opted to preprocess the style-sheet and distribute it with our theme.

Tangentially, I did not use sass even for prepocessing as I found it to be slightly wrong (It breaks rules that refer to html and body, we do not simply want to add the class in front of these). That's why I made https://github.com/StreamHPC/simple-css-selector-transform. The idea was to integrate this to doxysphinx, but I ended up just pre-processing the sources in the interest of time.

More importantly I replaced references of html.light-mode with html[data-theme=dark] which is how pydata-sphinx-theme switches the theme, so the doxygen-awesome dark-mode is kept in sync with the rest of the site.

The rest is just slightly different choices compared to the demo in doxysphinx, for example I chose to hide the titles from the doxygen html and instead use the sphinx ones, which I think integrates better with the rest of the site.