Kyoukara/FlycerUI.lua — reverse-engineered prompt

I want a small Lua UI toolkit called FlycerUI that lives in a single file and is easy to drop into another project. The goal is to let someone build a clean interface without a lot of setup, with a simple and friendly API for creating a main window or panel, adding text, buttons, toggles, sliders, input fields, and other basic controls, then reacting to user actions with callbacks.

Please keep it lightweight, readable, and pleasant to use, not overly complex. I would like sensible defaults for layout and styling so the interface looks decent right away, but it should still be easy to customize colors, titles, and sizes. Add a short example that shows the normal usage from start to finish, and write a minimal README that explains what it does and how to use it.

If the exact details are unclear, make reasonable choices and keep the first version focused and polished instead of trying to do everything. You can look up current Lua docs or common UI patterns online if you need to.