The `lit-css` repository provides build plugins for importing CSS files as JavaScript tagged-template literal objects, primarily for use with libraries like `lit-element` and `@microsoft/fast-element`. It's designed for developers who prefer writing CSS-in-CSS and want to streamline their workflow, though it's noted that this package may become obsolete once the CSS Modules Proposal is implemented. The project includes plugins for various build tools like esbuild, TypeScript, Rollup, Webpack, Vite, and Parcel.