匹配所有的最后一个子元素

node2:/var/www/html/js#cat h24.html 
<ul>
<li>aaaaaaaaaaaa</li>
<li>bbbbbbbbbbbb</li>
<li>cccccccccccc</li>
<li>dddddddddddd</li>
</ul>
<script type="text/javascript" src="jquery-2.2.2.min.js"></script> 
<script type="text/javascript" src="h24.js"></script>
node2:/var/www/html/js#
node2:/var/www/html/js#cat h24.js
$('ul li:last-child').css("background","red")
node2:/var/www/html/js#