originating (原始) 元素是什麼？ Generated Content Pseudo-elements: ::before and ::after. ... <看更多>

Like their name said it, :before & :after are used to apply css properties JUST before/after the content WITHIN the matching element. ... <看更多>

The draft spec for CSS4 pseudo-selectors still state that ::before and ::after must have a content property with a value that is not none, ... ... <看更多>