I can't say without seeing the actual page.
I'd suggest that you check into some tools that will help you diagnose issues like this. Internet Explorer has the F12 Developer Tools built in. There's an add-on available for Firefox and Chrome called WebDeveloper Tools. Both of them will let you dig into the CSS settings to see what the browser is using for any selected element and will give you visual cues to show the boundaries involved. Most of the time, this is enough information to discover what the problem is and how to repair it.