I don't consider that a remotely relevant argument. CSS is intended to style webpages at all times, webpages which are dynamic; CSS has never had a 'purpose' of rendering once and only once since oh, I don't know, 1997 or so. You might as well object to the _Magic: the Gathering_ example because it assumes a human to play each card mechanically; or you might as well object to the very first Turing machine in Turing's paper because he asks us to assume a setup where it's a human (or 'computer' as they were then known as) following the instructions mechanically.