jquery 获取id

node2:/var/www/html/js#cat a15.html 
<p id="green">tt</p>
<p id="tt">nnnn</p>
<p id="red">tt</p>
<p id="tt">uuuu</p>
<p id="tt">nnnn</p>
<script type="text/javascript" src="jquery-2.2.2.min.js"></script>    
<script type="text/javascript" src="a15.js"></script>
node2:/var/www/html/js#
node2:/var/www/html/js#cat a15.js
$('#tt').css("color","red");