... already in place). There is cpu usage/time overhead; the client needs to run the code to generate these classes every time the page loads. There is code bundle size overhead; the client needs to receive a CSS parser in order to generate these class names, and shipping this makes the amount of js the client needs to parse larger. Eval-ing out code at compile time that will be baked into the runtime code, for instance, to get a list of directories in the filesystem.