How to make tweets give external link message


I am using a twitter widget to show the tweets in my website. But how can I would like to add a class to them so that they display a message warning that you are going to an external site when the user clicks on them. I want the class “ext” to be on each twitt, but it doesnt happen.

Below is my code.

<div class="ext">
<a class="twitter-timeline ext"  data-chrome="nofooter noscrollbar noborders nofooter transparent"    href=""  data-widget-id="266166506696622080" target="_blank">Tweets by @FAFSA</a>
    <script>!function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0],p=/^http:/.test(d.location)?'http':'https';if(!d.getElementById(id)){js=d.createElement(s);;js.src=p+"://";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs");</script>

Thank you