possible? yes, easy? well no, depending on how good or bad you are with html and especially CSS. Basically what you have to do is to put your banner in a div layer and position the layer accordingly over the navbar. Parts of your banner also need to be transparent so that when it overlaps, it doesn't block what is underneath it.
If you are not familiar with CSS I suggest you visit this link,
http://www.w3schools.com/css/css_positioning.asp, or just search google for "css positioning"
good luck.