I think gloss is best explained by playing around with it. Theme's are very powerful, but hard to grok without seeing them. So, this.
npm i -g motion
cd gloss-demo
motion
Specifically, check out the pane.js file. I'm not claiming it's good or even ok code, because I'm extracting it extensively from a bigger and more arbitrary file. But, it does sort of show a few pieces of theming.
To me, themes are something I can't go back to now having. Being able to re-style multiple elements is a fundamental thing you need when making robust views. And doing so with many-layered conditional statements, or imperative function calls is a mess, and a big step back from CSS.
In this demo unfortunately there aren't any really complex uses. Only one theme actually re-styles multiple elements. But it is a little sandbox you can start with and play around.
Button shows a more complex theme, which takes bordered and color as it's two themes. Again, it only re-styles a single element, so not the best use case, but it does show mixing two different theme props.
