        <p>The navigation links at top of a Web page are all entries in a menu implemented using HTML, CSS, and Javascript. When the navigation bar is expanded, the navigation links are available to the user. When the navigation bar is collapsed, the links are not available.</p>
         </section>
         <pre xml:space="preserve">
...

  &lt;script type="text/javascript"&gt;
  function toggle(id){
    var n = document.getElementById(id);
    n.style.display =  (n.style.display != 'none' ? 'none' : '' );
