DouyinFE/semi-design ? reverse-engineered prompt

Build me a modern React UI library and design system site like Semi UI, with a clean documentation experience and a good set of reusable components for real app building.

I want the library to include common components like buttons, forms, inputs, modals, tables, navigation, feedback, and layout pieces, all styled consistently, keyboard accessible, and ready for light and dark mode. Please make it support theming with design tokens so the look and feel can be customized without rewriting components. It should also be friendly for server side rendering and feel polished across modern browsers.

Add a docs and examples site where I can browse components, see live demos, and quickly understand how to use everything. If useful, include a simple way to switch themes and show how design tokens affect the UI. Use current docs online if you need to, and make sure the codebase is organized, well tested, and easy to extend later.