On your "Showcase" page http://www.mapsmarker.com/showcases/2/ at the very bottom, I've spotted that the "Die Seele der Stadt" page has customized the window that pops up when you click on one of their markers. (Dark background, White letters with tabs for video and audio)
How is this done?
I've also noticed that you are using my site as a demo on your "Showcases" page:
My Travel Destinations
I feel honored that you are using my page as a demo to showcase you product, but you do have the wrong link up. I have since changed it from:
I promise that I won't change the Permalink again.