$(document).ready(function(){
$("button").click(function(){
$("h1,h2,p").toggleClass("blue");
});
$("#changecss").click(function(){
$("#myid").css("background-color","yellow");
$("#myid").css("color","blue");
});
});
<h1>Heading 1</h1>
<h2>Heading 2</h2>
<p>This is a paragraph.</p>
<p>This is another paragraph.</p>
<button>Toggle class</button>
<p></p>
<div id="myid">
this is the text which i want to change the css usign the jquery
</div>
<input type="button" id="changecss" value="change css">
.blue
{
color:blue;
font-size:12px;
}