black banner problem

Hi guys,

When I open my my website in full size there isn’t a problem. But when I open it in a smaller size the banner only fills the part you can see instantly. So when I scroll to the right the banner suddenly stops and there is just an open space next to it.
Don’t know if this makes any sense but take a look at it for yourself:
http://www.riadtachata.com
I’m guessing I’ll need to change something in the stylesheet but I’m not sure and I have no clue where to look. Any of you know what do?

Greets,

Niels