Live Example: (Read the CSS Newbie article)

Source Code: (Save the Source)

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<title>CSS Newbie Example: Test for Border-Radius Support</title>
<script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.4.2/jquery.min.js"></script>
<script>
jQuery(function() {
   jQuery.support.borderRadius = false;
   jQuery.each(['BorderRadius','MozBorderRadius','WebkitBorderRadius','OBorderRadius','KhtmlBorderRadius'], function() {
      if(document.body.style[this] !== undefined) jQuery.support.borderRadius = true;
      return (!jQuery.support.borderRadius);
   });
});
$(function() {
   if($.support.borderRadius) { 
      $('#infobox').text('Hurrah! Your browser supports border-radius! Enjoy!');
   } else { 
      $('#infobox').text('No border-radius support. What a square browser! (get it?)');
   }
});
</script>
<style>
body {
   font: x-large/1.4 Georgia, "Times New Roman", Times, serif;
   text-align: center; }
#infobox {
   width: 400px;
   margin: 20px auto;
   padding: 20px;
   color: #333;
   background-color: #09c;
   border: 4px solid #333;
   /* Our massive border-radius stack. */
   -moz-border-radius: 10px;
   -webkit-border-radius: 10px;
   -o-border-radius: 10px;
   -khtml-border-radius: 10px;
   border-radius: 10px;
}
</style>
</head>
<body>
   <p>Test in different browsers to see the results.</p>
   <p><a href="/test-for-border-radius-support/">View the original article.</a></p>
   <div id="infobox">
      The results go here.   
   </div>
</body>
</html>