How Do I Change the Background Color of the Drop Down Hover Menu in the Header?

ul.dropdown-menu {
 background: #000000

 

!important;

Here's how to apply the code: 

1. Login to your admin
2. Go to Storefront CMS 
3. CMS Features
4. Theme Settings
5. Custom CSS tab
6. Copy the code in blue above and paste it at the top or bottom of the "Global Custom CSS Code" box. 
7. Save/Update Layout 
8. Go to your storefront, refresh, and the 3 default images will be removed