#special-id 匹配ID为special-id的元素

#special-id           匹配ID为special-id的元素                     在CSS中

node2:/var/www/html/js#cat h13.html 
<a id='ffff'>aaaa</a>
<a id='gggg'>bbbb</a>
<a id='gggg'>bbbb</a>
<a id='hhhh'>cccc</a>
<a id='llll'>dddd</a>
<div id='gggg'>uuuuuu</div>

<script type="text/javascript" src="jquery-2.2.2.min.js"></script>    
<script type="text/javascript" src="h13.js"></script>
node2:/var/www/html/js#cat h13.js
$("#gggg").css("background","#bbffaa");