Here is the site:

In the part "Reference" when I click on "Vanjske ograde", "Unutarnje ograde", ... Firefox, IE6 and 7 and Safari drop down the corresponding gallery, moving bottom content down.

Opera has problem: when I click, it moves bottom content up overlapping gallery content.

How can I solve this problem?

(I don't know if i should put this in JavaScript or HTML and XHTML section, but I think it has to be JS)

Thanks in advance!