CSS 基礎系列：僞類和僞元素

1.僞類和僞元素的引入 CSS introduces the concepts of pseudo-elements and pseudo-classes to permit formatting based on information that lies outside the document tree. CSS 引入僞類和僞元素的概念是爲了格式化文檔樹以外的信息。也就是說，僞類和僞元素是用

>>阅读原文<<