CSS-like `Border` about egui HOT 1 OPEN

In WPF/Avalonia there is a type called Brush, which is used for the foreground, background, and stroke properties on the widgets. It can be a solid color, a gradient, a texture etc. In .NET this is done through polymorphism everywhere (every class in WPF has like 9 abstract parent classes), but maybe egui could do the same with an enum? We would still be packing 24 bytes per field instead of 4 (if every variant other than Color32 is boxed), but maybe it would be worth it for the flexibility.

The extra variants could also be behind a feature, so the size becomes 4 bytes when it is not active. But then it has to be marked #[non_exhaustive], otherwise enabling the feature would cause a SemVer breaking change, and that goes against the API guidelines since features have to be additive.

from egui.