tailwindlabs/tailwindcss ? reverse-engineered prompt

Build me a utility-first CSS framework that lets me rapidly build custom UIs without leaving my HTML. The main idea is to avoid writing custom CSS and instead use a big set of pre-existing classes for everything from padding and flexbox to colors and typography.

For example, I should be able to style a button by just adding classes like bg-blue-500, hover:bg-blue-700, text-white, font-bold, py-2, and px-4 directly to the element.

The system needs to be smart. It should scan my HTML and JavaScript files, find all the utility classes I'm using, and then generate a single, highly optimized CSS file that only contains the styles I actually need for that project. It must also have responsive design helpers, so I can apply styles at different breakpoints using prefixes like md: or lg:, and support for dark mode.