Topic: Navigation button OVER thumbnail image

I need to place the navigation arrow over the thumbnail area.

My thumbnails are 50x50 pixels and i changed the design of the arrow in a 50x50 square with an arrow in it (the style from the website)

The problem is that that arrow shows below the thumbnail area. I tried to place it on a higher layer but it still shows below the thumbnail.

Same problem when i place a an image OVER the main image area. It shows below the image.

How can i change this? And where?

Thanks in advance.