How can I get rid of the lines that separate the header's background image from the rest of the header's background? I have a nice blue background image for the header, and I’ve set the background color to match that exact same shade of blue. However, there are visible lines separating the image from the background color on both sides—I can’t seem to get rid of them, and I want the header to look like one seamless, full-screen element. Is this possible?