CSS-'popup'-effects (with :hover pseudo-class) on nested boxes may cause
Opera 7 to only partially display the inner boxes if the outer box has an explicit width.
Update: in build 3144 (7.2) the 'popup' doesn't work at all, due to bug 16
A workaround is specifying position:relative for the outer box.
Move the mouse over the text in the gray box below.
This is how it displays in Opera 7.1