Recently, I worked on implementing a dark theme in a web app. I used a bunch of new-ish CSS things (variables, masks, filters) to put it all together, and I was amazed at how quickly it went. I just wrote it up here in case it’s useful to others:https://medium.com/@mwichary/dark-theme-in-a-day-3518dde2955a …
It’s a good question. I didn’t have to worry since the app was an Electron app. The variables part won’t fall back and would have to be accompanied with manual colour assignment (or a CSS preprocessor). Masks are also not a progressive enhancement in this shape.