CSS伪类随记笔记,目标伪类、元素状态伪类、动态伪类、nth-child(数字)、nth-child(n)、nth-child-强调、nth-last-child(数字)、nth-of-type(数字)、nth-of-type(n)、nth-last-of-type、only-child、empty、否定伪类、first-line-letter、before和after