When the navbar wraps around, hover menus are overlapped by lower row of buttons

Hi, I ran into this problem when building my website.
I had made a number of pages with their "" as their parents, and at some point they wrapped to another line. However, when I hover over the navbar items in the first row to see their children, the list is obscured by the items under it.

I've poked around with the "Inspect Element" function in my browser, and it seems like it's due to the reason that the items on the bottom row are defined later than those in the top. I would think a solution would be to change the "z-index" css fields in the divs so that the previous items have greater priority. However, upon looking around the source, it seems that the html/css code is handled through the "theme" function, referenced in [marinelli root]/template.php, of which I could not find the source.
(TL;DR I need to change the z-index css field in the menus, but I don't know how)

How would one fix this problem?

(and thanks in advance)