Wary as I am to attribute to malice what can be explained by incompetent journalism, the fact that Sanguine Security are mentioned by name in the article, and their website directly linked to, makes me think this must be a paid marketing piece. The article also seems to imply that Willem de Groot is the person describing this "feature" as a modern addition to the CSS spec (it isn't any such thing).
There is no such feature, this attack uses JS eval normally and does not rely on anything special in CSS the language. There isn't anywhere near enough novelty here to describe this as anything distinct from any other old-fashioned XSS.
Flagged.