Note Box

Hello all,

I have been trying to write a docbook file. I am using <note> element. 
But I cannot see the note box (or borders). What am I missing here? Here 
is my code.

<?xml version='1.0'?>
<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
                   "http://www.oasis-open.org/docbook/xml/4.5/
docbookx.dtd">
<book lang="en">
<bookinfo><title>My first DocBook document</title></bookinfo>
  
  <chapter>
    <title>TEST DOCBOOK</title>
    <note>
        <title>This is Note</title>
        <para>This is test.</para>
      </note>
  </chapter>
</book>

Thanks.