<script type="text/javascript" src="/js/jquery.js"></script>
<script type="text/javascript">
$(document).ready(function(){
$(".btn1").click(function(){
$("p").animate({fontSize:"3em"});
$(".btn2").click(function(){
$("p").animate({fontSize:"1em"});
<p style="background-color:yellow;">This is a paragraph.</p>
<button class="btn1">Animate</button>
<button class="btn2">Reset</button>