For those of you like me who prefer light text on a dark background out of preference or to reduce glare or whatever probably already have a number of browser extensions or add-ons to achieve this sort of thing. Sometimes they’re not so great, but we make do.
There are, of course, many options in multiple browsers for loading custom CSS files to override the settings of commonly visited websites. The most well known being Stylish, which is available for most browsers, though not for Internet Exploiter.
That includes a number of dark themes for use with any website running Discourse. Some of them state that they’re for specific sites which run Discourse and are probably able to be tweaked slightly to work here, but there is one generic dark Discourse theme which I can assure everyone does work here somce I’m using it now. Previously I used my own, horribly bloated thing which had been generated from another script which inverted the colours, but had lots of problems (hence never sharing it). This one, however, is far more usable.