Only black background in full width module Top-b

I have bought and installed JP-Interior.
No I will show an full width image at position Top-b.
I have read this topic about adding a full width at postion bottom-b:
www.joomlaplates.com/forum/j3-interior/5...ition-bottom-b#12742

So I have added that lines to the theme.css (changed the position bottom-b to top-b).
Then I have created a module at position top-b, which is showing one image.
The result is a black bar full width at the position Topb-b but no image.

You can see a live URL of my test site here:
rommersbouw-d-o-t-nl.alvast-online.nl/

What can I do to show an image full width at position Top-b.
I will show at some other menu-items other images at the same position, so changing the background image in the template setings is not enough.

Hi there,
1.) Upload your image to your images folder
2.) Add this css code to your css/custom.css

#top-b {
background-image: url("../../images/paper.gif");
}

We are committed to help you with any type of support query, however we can't provide extensive help in terms of customizations. In general customizations may look simple but you will require solid knowledge of web technologies and programming skills to do them or hire a professional who can do it for you.

Thanks for your reply.
It works fine in the way you described.
But in that case the image at position Top-b is in every menu item the same.

That's why I asked this:

I will show at some other menu-items other images at the same position, so changing the background image in the template setings is not enough.

What is the best way to fix this?

I hope you can advice me.