Good stuff, thank you for sharing.
This is for users who prefer dark themes who are overriding styles of websites incorrectly. It is a failing of the user's browser/OS for not explicitly overriding both background and color at the same time or neither. If every developer had to add in a color for the edge case that someone is overriding styles globally, then we'd be bloating stylesheets with extra unnecessary bytes.
WCAG doesn't specify implementation, but WCAG 1.4.3 does require a minimum contrast ratio[0]. If the site allows black text on a black background, it will fail that requirement.
0 - https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-cont...
That's done on purpose to discourage people from posting (or reading) them too often. PG was afraid letting people write text posts would lead to "blogging."
There was never any real chance of this forum going mainstream, not because it was too ugly and awkward but because it didn't have any mainstream appeal. Negative reinforcements like making the text purposely difficult to read mostly just punish existing users.
Still, I can't seem to be able to collapse thread branches because it requires javascript. That's a shame.
I wonder if w3m would recognize something like:
.collapse:checked + .content-and-replies-container {
display: none;
}