Every modern programming language has a facility for creating modules, or external libraries. Modules allow you to break a program apart, making it easier for multiple people to collaborate, and for programmers to concentrate on smaller, more easily solved problems abstracting away larger and other issues. Even JavaScript, which has famously failed to include modules for many years, now has such a facility. But CSS, which allows us to describe the design of Web sites, is not modular, which means that definitions are repeated, spread across files, and are generally less organized and abstract than they could be. In this talk, Glen Maddern describes work he has done toward creating CSS modules, including how they work and can benefit developers and designers.