Marcin Wichary has written a great piece that dives into how he used CSS Variables to create a night mode and high contrast theme in an app. There’s so many neat tricks about how to use CSS Variables (Chris has also looked at theming) as well as how to organize them (Andras Galante has an interesting take on this) in here. Plus, Marcin shares some tricks about using filters to invert the color of an image.
I also also love this part of the article where Marcin writes:
I was kind of amazed that all of this could happen via CSS and CSS alone: the colours, the transitions, the vectors, and even the images...
CSS is mighty powerful these days, and it’s posts like Marcin’s that remind me it wasn’t that long ago that theming an app like this would’ve been impossible.