Accessibility Improvements (Autism, ADHD, SPD, etc.)

I have a few suggestions for improving the user interface (UI) of Khan Academy and would like anyone to add on whatever ideas they have.

1. Themes (dark and pastel). I know there are a ton of requests for dark themes, and yes I have up-voted them all, but I would like to reiterate it here as a principal of universal design. Allow changing the overall color theme to reduce eye fatigue and improve concentration. I would prefer a dark grey theme, but others might want dark blue, and as this post brilliantly points out on modern OLED screens a pure black background would save a ton of energy. It's much easier to stare at a screen for a long time if it's not white. Also some dyslexics prefer different color themes and certain fonts, particularly pastel. If you are on a public computer it may be difficult or impossible to change it on a browser level so an option in settings would be awesome.

2. Written Lessons: Increase the amount of written summaries in math. As an autistic, I personally process written information much easier than verbal information, and other autistics (or people with sensory processing issues) have said that they often use subtitles on videos. More options for how to present the same information would allow a diverse student population to find what works best for them.

3. On the topic of subtitles, often I have to toggle them on and off repeatedly because the text covers important information on the video. This is a major pain, but I don't know what could be done other than leave a small bottom border on future videos. This awesome post mentions how to change settings on YouTube subtitles so that may help some people a bit.

4. Non-Graded Review Options (PLEASE!!!). I have ADHD as well and need to periodically review material. I currently know of no option to review the material without losing my progress if I make a mistake. It feels like a huge liability to go back and knock the rust off when I know I'm going to get a few wrong at first. I would like a review challenge, something like a mastery challenge, where when whatever questions I get wrong I can have the option of reviewing the material with practice questions, without it affecting my progress/grade.

That's all I can think of right now, but please add in ideas of you own. Thanks :)