Paste that into uBlock Origin:

news.ycombinator.com##html:style(filter:invert(100%) hue-rotate(180deg)) news.ycombinator.com##body:style(background: white) news.ycombinator.com##div.toptext:style(color: black) news.ycombinator.com###hnmain td[bgcolor="#000000"]

Not my idea, I took it from a comment on HN a few weeks ago.