是否有任何方法可以只使用CSS来显示实时日期或时间?

A friend of mine claims he knows how to display a variable, in this case time of day in H/M/S format as well as the date, using only CSS. He "forgot" what the code was, and thus couldn't tell me. It seems a bit hard to believe that this would be possible; but I'm curious nonetheless as to wether this can be done. Any ideas?A friend of mine claims he knows how to display