I created a simple HTML5 header structure, which contains a paragraph (#logo) and an unordered list (#menu, nested in a nav element).
The header contains more elements, so it has a white background, while the #logo and #menu elements share the same background-color (#369). This works fine in all major browsers (Firefox/IE 8/Chrome/Safari). In Mobile Safari (both iOS 3.2/iPad and iOS 4.1/iPhone), there is a thin line between the #logo and the #menu element, although the margins have been set to 0 for both elements.
I am grateful for any advice on how to avoid this effect. The HTML/CSS code is at http://janeden.net.