It's done with jQuery:
Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<style type="text/css">
#content_to_fade_in{
display:none;
}
</style>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4/jquery.min.js"></script>
<script type="text/javascript">
$(document).ready(function(){
var fade_duration = 1000 // milliseconds
$('#content_to_fade_in').fadeIn(fade_duration);
});
</script>
</head>
<body>
<div id="content_to_fade_in">
<h1>I am fading in.</h1>
</div>
</body>
</html>