Change Navigation on Hester

Site URL: https://www.thiscitymaps.com/

How do I change the background of the text so that it is opaque instead of transparent. When I click the dropdown for the menu on the side it shows up like this and is hard to read. 

Note : this only occurs in mobile or when you have the browser window small enough that the pages do not have room to display at the top of the page. I am using the Hester template in 7.1

thiscitymaps.com 

Add to Home > Design > Custom CSS

@media screen and (max-width:767px) {
.header-menu-bg.theme-bg--primary {
    background: red !important;
}
}