Dark mode themes for websites and software are very popular, and for good reason. Unfortunately, it is often done very poorly and actually leads to worse eye strain than most light themes. This is, in my opinion, due to the fact that many designers have made the error of thinking that "dark = white text on black background" or "dark = inverted light", leading to dark themes which painfully high contrast that leave your eyes strained (and at least for me, with persisting "bars" across my vision for a few minutes) after a minute or two of reading.
What works better is very light grey on a darker (but not close to black) grey background. But I prefer a pleasant dark grey on pale blue background :)