White background for the container of my index menu

I am using the Henson Template. I am happy with the look of the desktop platform. 
However the overlay of the index links on the Mobile platform is not readable.

is there a way to make the container of the index menu links white without changing the look of my desktop/ipad platforms.

attaching screenshots of the mobile vs. the desktop

Misread the question the first time @cvan. Try this in Custom CSS to add a white background to those links at the bottom on mobile.

@media only screen and (max-width: 640px) {
nav.index-navigation.collection-nav {
    background-color: #ffffff;
}
}

amazing--this worked! thank you!