Change Color of Menu Header/Background (Mobile) for Lusaka Theme

Site URL: https://www.artslosaltos.org/

I'm trying to change the Menu Dropdown Color for the Header and Background for Mobile Only. My theme is Lusaka and I've tried to inject custom css but it doesn't seem to be working. Currently, the Menu Header and Page for Mobile is White and I'd like to change it to Black or Orange. 

Thanks in advance. 

 Add to Home > Design > Custom CSS

.header--menu-open .header-menu-bg.theme-bg--primary {
    background: orange !important;
}