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 (a-tag of class "flxMenuToggle").
When the bar has focus, you can use the "Arrow" keys to navigate through the menu.
The [ESC]-button will close the popup menu.