Shaw and Chris talk CSS Modules, a rather old bit of technology in the CSS-in-JS category. CodePen now supports them, which took a little work because the way they process code is a smidge unusual.
We use CodePen Modules (with Sass!) here at CodePen so we knew we wanted to support them, but we got a little push when GitHub blogged about how useful they find them, and lots of folks raised their hands saying they still use them too.