[Theme: Virtue] Dropdown menu overrules certain portfolio items

The first is I think a fault in the dropdown menu.
When I am in a portfolio-page with different items, and I use the dropdown menu, it dissapears when I go over a dropdown menu item when a portfolio item is under it. Is there some simple code to keep the dropdown menu on top of all the portfolio-items? This doesn’t happen now.

Thanks in advance, it will be a big help!!

Gerard