That thread is 5 years old, and nothing really came out of it.

The genius solution in there is probably this one:

     @media (prefers-color-scheme:dark){body{filter:invert(1) hue-rotate(180deg)}}

...which you can try by doing this in the browser console:

    const styleElement = document.createElement('style');
    styleElement.type = 'text/css';
    styleElement.textContent = "@media (prefers-color-scheme: dark) { html { filter: invert(1) hue-rotate(180deg); } }";
    document.head.appendChild(styleElement);

But I get that there are a lot of opinions. Just try one, put up a vote over a week, do it over 4-6 weeks, settle on the one that has the best feedback...