I'm currently in the process of improving my sites Hugo theme. I removed features I never used and simplified unorganized HTML and CSS, to enable adding new features (like better support for IndieWeb things) later. My theme was once based on the Hugo theme Mainroad, but I modified so much over the time that almost nothing is left from the original theme. The theme, which was a port of a WordPress theme called “MH Magazine”, supported Internet Explorer 11, but when I discovered CSS variables, I made use of them and broke Internet Explorer support on the way.
I generally prefer dark user interfaces wherever possible. My phone is set to a dark mode (as far as there is a dark mode in Android Pie), apps like Telegram are set to dark mode and on the desktop I prefer dark modes too. But the most important software I use everyday is a web browser. And most websites don't support a dark mode yet (because there was no native browser feature for that until recently).