cssmodules

CSS Modules are CSS files in which all class names and animation names are scoped locally by default. They compile to a low-level interchange format called Interoperable CSS, but are written like normal CSS files. The ability to explicitly state dependencies eliminates the need to avoid naming conflicts in the global scope.

For a more colorful introduction, see this blog post, which was written by one of the authors of the project near the time of its release.