SiriusSoftwareLtd/rayfield-gen2 ? reverse-engineered prompt

Build me a polished Rayfield Gen2 style UI library for Luau that I can drop into a Roblox project.

I want it to feel modern, clean, and easy to use, with a simple way to create windows, tabs, sections, buttons, toggles, sliders, text inputs, dropdowns, and color pickers. Make the default styling look premium, with smooth animations and a good layout, but keep it easy to customize so I can match my own theme.

Please include a working example so I can see how to use it right away, and make sure the code is organized, readable, and ready for testing. If you need to check current best practices or docs online, do that. Also add any basic validation or quality checks that would help keep the project stable.