Adding a light theme (e.g. for accessibility users)

[triesmon]

I'd like to add a light theme to support accessibility users. Some users with vision needs depend on websites offering a standard light mode option because their browser accessibility settings are tuned for an internet that is mostly light mode, navigating to an outliar with dark mode can create a disruptive browsing experience.

Here's a relevant issue/request.
#1793

Here's what an implementation could look like. It's around a 500-600 line change. Made it as targeted as I could.
triesmon#2

Would anyone be open to this? I understand a separate stylesheet can be annoying to maintain.

What changes would you want to see here?