$(document).ready(function(){
$("p").filter(".intro").css("background-color", "yellow");
});
/*
<h1>Welcome to My Homepage</h1>
<p>My name is Donald.</p>
<p class="intro">I live in Duckburg.</p>
<p class="intro">I love Duckburg.</p>
<p>My best friend is Mickey.</p>
*/