conceptadev/mix ? reverse-engineered prompt

Build me a Flutter styling system called Mix that lets me keep style definitions separate from widget code, but still use them in a clean, type safe way.

I want a fluent API for styling boxes and text, with reusable tokens for things like colors and spacing, plus support for merging styles, conditional variants like hover, pressed, dark mode, and breakpoints, and simple animations and modifiers when needed. It should feel natural for Flutter developers, work with normal widgets, and stay flexible enough to use outside Material Design.

Please include a few clear examples and a small demo app or sample screens that show how to style cards, buttons, and tag clouds the Mix way. If you need to check current Flutter or Dart docs online while doing it, go ahead.