Zinnia: Fix for See-Through Dropdown Menu

I have my main pages running lengthwise at the top of my website. Some of the main pages have sub-items that are displayed with short drop-down menus.

This hasn’t been an issue until this evening, when the list of main pages at the top of the website went from one line to two. When I hover over a link to a main page that has sub-items (such as Produce High Webcomic), the drop-down menu is see-through and shows the second line, making the drop-down look cluttered, difficult to read, and just not attractive or professional.

This seems to be an issue only when I view the website using a PC.

Any suggestions?

Thank you!

Website: http://www.happimessmedia.com
Theme: Zinnia Child Theme