## 4. 伪类选择符 ### E:link ### E:visited ### E:hover ### E:active ### E:focus ### E:lang(fr) ### E:not(s) ### E:root ### E:first-child ### E:last-child ### 3E:only-child ### E:nth-child(n) ### E:nth-last-child(n) ### E:first-of-type ### E:last-of-type ### E:only-of-type ### E:nth-of-type(n) ### E:nth-last-of-type(n) ### E:empty ### E:checked ### E:enabled ### E:disabled ### E:target