Example of a responsive navigation bar.
When the viewport's width is less than 600px the bar will turn into a toggle button.
If you push the button a popup menu will slide in from the top.
Other than the default button, this toggle button is an explicite code definition.
HTML:
<div id="exmp1Trigger">
<a href="javascript:" title="open" class="flxMenuToggle">MENU</a>
</div>
When the bar has focus, you can use the "Arrow" keys to navigate through the menu.
The [ESC]-button will close the popup menu.