Sure, you could get rid of CSS, but in favor of what? You probably need something just like flexbox, and it's not easy to beat an optimized implementation of CS

Sure, you could get rid of CSS, but in favor of what? You probably need something just like flexbox, and it's not easy to beat an optimized implementation of CSS flexbox in terms of layout performance (especially if parallelized). You could eliminate the restyling step by not having cascading and selector matching, but that hurts productivity and maintainability, which is why you see frameworks like GTK+ moving toward CSS-like styling. There's no free lunch here...