Menu's overlapping

I have a horizontal CK Maximenu with dropdown sub menus in the menu position of Cassiopeia. In the top-a position I have another Vertical CK Maximenu. The submenu of my main menu is behind the menu in the top-a position - how can i change this. I have tried to chnge z values but no change at all.

Sorry - now i found the problem. I had to bring the header div forward with a large z-index!