When i click on "My account" on top menu, the menus pop up but they stay behind other divs. This happens on many pages, not just on homepage. I attach screenshot to show the problem

I am not able to reproduce on Demo site.
Can you provide URL? Have you done some custom mods?

No custom mods, just installed some plugins i bought from here (you). Anyway i was able to solve it by modifing this:
header .relative2 {
    border-bottom: 1px solid #dfe3ed;
    padding: 4px 25px;
}

to this:

header .relative2 {
    border-bottom: 1px solid #dfe3ed;
    padding: 4px 25px;
    z-index: 999;
}

So its okey now, the menu came in front

@KaloSex
Try to use z-index with least value possible, first try if it does not work with value 9, 99 , 199 etc... to avoid conflicts with other functions.