Blue bars around banner [Solved]

This thing is hard to explain because I'm not sure what's the problem. But let's try and hope someone understands me.

The Problem: No matter what kind of banner I put on the top of my forum, it leaves annoying blue bars on top and bottom, left and right. This blue color is the gradient color that comes with the default theme (phpbb3 / ProSilver). Like this:

The Question: How can I remove those blue bars and make only my banner visible? For example on this site the banner is showing just like I'd wanted it to show on my forum too.

You probably noticed that I'm a total rookie with this whole phpbb-thingy BUT I really would appreciate if someone helped me through.

If you resize the banner larger, it's possible that it might clear that.

Broly Ss10 wrote:If you resize the banner larger, it's possible that it might clear that.

that does fix it, i did just that with mine to make it fit

Broly Ss10 wrote:If you resize the banner larger, it's possible that it might clear that.

If i make the banner more wider it breaks the layout on the right side. No matter how big my banner is it just keeps adding those blue bars on top, bottom and left (and on the right side it goes "over").