Global dark mode

[oliverfencott]

This PR expands on the previous dark mode work and includes a fix provided by @elfenermarcell.

There are effectively 3 changes implemented:

1. Fixes an erroneous CSS declaration for text-indent across all occurrences (with some minor whitespace formatting in applicable files).
2. Collapses all dark mode rules into a single media query in each .css file.
3. Appends the above CSS query to every .css file in static to enable dark mode across all versions of documentation.

Please note that 3. was done by a script that simply appends a string to all .css files that match (docpage.css, landing.css, main.css). I may have overlooked something obvious when doing this due to my lack of familiarity with the build tools and project structure.

[sogaiu]

I clicked through to see the results for the "Data Structures" page [1] and the "Parsing Expression Grammars" page [2] for all of the versions linked at the top of the pages (the links that come after "Other Versions").

It looks pretty good!

@elfenermarcell How does it look to you? May be this PR sufficiently addresses things that #278 was meant to attend to?

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If anyone else is interested in seeing the changes, the "Data Structures" page is easier to see effects of the changes for the tables as scrolling may not be required (^^;

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[1] http://localhost:8000/docs/data_structures/index.html

[2] http://localhost:8000/docs/peg.html

[elfenermarcell]

Looks correct. The tables look right in dark mode, and dark mode works in every version. I'll close my PR #278.