What's the easiest way to create a styled app?

Question

Java

Good day!
I'm interested in what tools now allow you to most easily create stylized cross-platform applications (preferably with some kind of ready-made basic set of styles).
For the most part, solutions for C ++ (like Qt) and C # are of interest, but Java is also possible.
If possible, I also ask you to throw off a couple of links to examples, thanks!

Answer 1

Qt. Look at the Telegram client. Seems good, doesn't it?
Qt has the ability to control appearance with a CSS-like language.

Answer 2

sciter.com

Answer 3

QtWidgets
QML