Do you notice that even though the 2nd square has been hidden, the browser still draws the boundary box for that element? It doesn't collapse the space. However, the 3rd square, a red one, has been positioned absolutely. What happens when it's hidden? It disappears! Check out "View Source" and you'll see there are SIX colored squares here. One is hidden, but it's position remains (relative positioning); one is hidden, and it's space is collapsed (absolute positioning).