Came here to say exactly that: CSS was designed to be friendly and just ignore any line it doesn’t understand. It’s the whole point of browsers and progressive improvements.
Are we blaming the spec and the author of the post for trying to conform to the checks, instead of blaming Adobe or Kobo for using 16-year old technology that ISN’T spec-compliant? -.-
Yes. sometimes specs are badly designed. Targeting a constantly moving goalpost for a spec mainly implemented by embedded devices seems to me like, best case, questionable judgement