:nth-child(2)选取第几个标签，“2可以是你想要的数字”

.demo01 li:nth-child(2){background:#090}

:nth-child(n+4)选取大于等于4标签，“n”表示从整数，下同

.demo01 li:nth-child(n+4){background:#090}

:nth-child(-n+4)选取小于等于4标签

.demo01 li:nth-child(-n+4){background:#090}

:nth-child(2n)选取偶数标签，2n也可以是even

.demo01 li:nth-child(2n){background:#090}

:nth-child(2n-1)选取奇数标签，2n-1可以是odd

.demo01 li:nth-child(2n-1){background:#090}

:nth-child(3n+1)自定义选取标签，3n+1表示“隔二取一”

.demo01 li:nth-child(3n+1){background:#090}

:last-child选取最后一个标签

.demo01 li:last-child{background:#090}

:nth-last-child(3)选取倒数第几个标签,3表示选取第3个

.demo01 li:nth-last-child(3){background:#090}

:nth-child的这些用法在实际中很用得着，不用单独给需要选取的标签加上ID或Class

[CSS3] :nth-child的用法