True, though doing it in CSS does have a couple of interesting aspects, using :hover would filter out bots that didn't use a full-on webdriver (most bots, that is). I would think that using an @import with 'supports' for an empty-ish .css file would be better in some ways (since adblockers are awfully good at spotting 1px transparent tracking pixels, but less likely to block .css files to avoid breaking layouts), but that wouldn't have the clever :hover benefits.