remove unneeded heights and reduce banner file size

Created by: stwa

I wasn't able to remove the explicit max-height for .menu-wrapper, so I have increased the value to 25em to make sure there is no overflow. As it's the max-height property (and not real height) that shouldn't be a problem, the wrapper only grows to the size of its content. I removed some unneeded directives in the css which don't have any effect. Also I reduced the banner file size to ~217KB.