你有了解css计数器（序列数字字符自动递增）吗？如何通过css的content属性实现呢？

counter-reset

counter-reset: count 0  

counter-increment

counter-increment: count 2  

<ul>  <li>Item</li>  <li>Item</li>  <ul>    <li>Item</li>    <li>Item</li>  </ul></ul>

ul {  counter-reset: count;}li::before {  counter-increment: count;  content: counters(count, '-')'.';}

1.Item2.Item    2-1.Item    2-2.Item