I've been trying to, through my browser and extensions, set a custom font for all websites. Specifically Atkinson Hyperlegible (google fonts link), developed by the Braille Institute, since I find it much easier to read when parsing large blocks of text. I've heard from some dyslexic folks it helps them as well (more so than Open Dyslexic or Dyslexie).

Unfortunately, it seems to fall down on Beehaw! I think it gets overridden by the theme settings, and neither Firefox nor any of the font-changing extensions seem to be able to get past it.

Would it be impossible to add a version of the darkly and litely themes with Atkinson Hyperlegible as the typeface? Heck, it's good looking and as readable as it gets, it couldn't hurt being a default option!