Simple backgrounds for Joomla menu

I thought that this would be a cinch to do, even with my limited knowledge of CSS, but it's turning out to be a complete nightmare for some reason. I'm trying to make something like what's in the attached image: a horizontal menu in a module position that's 26 pixels tall. I'm using Joomla. I have two background images (the gray one and the white one, like in the image) that are each that height. I'd like the hover and active menu items to have the white background and the inactive ones to have the gray background. Everything I've tried has either not lined up properly (so that there's a gap between the background image and the top of the module) or come out to be vertical when I look at it in Internet Explorer, and I'm at my wit's end right now. The module position has no padding on it, so I'm not sure why there'd be a gap.