Megamenu drop downs horizontally centered?

I am using Shoutbox theme and there I have main menu as (megamenu) and it works like a charm.

The only problem is that all menu items drops as aligned left from their nav item and it is ok for the first and second item of course when counting from left. But when moving to third or fourth item, then their drop downs are overlapping the webpage main content area from the right side obviously. Looks terrible and is not usable at all.

You can imagine when clicking the megamenu link (I have width of 4 images in my drop down) that if it would be same megamenu in every link all the way to the right it would finally overlap. Like here, imagine ‘Dropdown’ would also be megamenu and continuing to the right:

Here is the theme preview (check Megamenu and Dropdown):
Megamenu

Is it anyhow possible to center all items that drops down, I mean the whole drop down? Centered in main content area, like header etc.

It is very weird that it is written to be aligned like this. Because it is just impossible to work perfectly but only in the most left link on page. Or when it only has one drop down item, it would work also in every where but here I have 4 items opening down from every link and I think it is normal amount.

I tried to find wrapper or what ever from css but nothing helps on this issue.

Please…….. help. Thanks.