Problems with navigation header

Hello,

My website is here. I’m having trouble with the top navigation. I installed the Dropdown Menu plugin by Shailan. I’ve replaced the regular navigation with the drop down menu. It installed and works fine however when I open up the website, the navigation is surrounded by a “white box” – which you can see.

I’m not much of a coder but I think it may have to do with the DIV. Could someone please help me?

Thank you in advance.