Utility-first CSS framework that won the framework wars. Tailwind v4 reset the engine to Rust; the de facto styling layer for shadcn/ui, Vercel, and most modern apps.
From Wikipedia
Tailwind CSS is an open-source CSS framework. Unlike other frameworks, like Bootstrap, it does not provide a series of predefined classes for elements such as buttons or tables. Instead, it creates a list of "utility" CSS classes that can be used to style each element by mixing and matching.