Changing Mobile Menu Overlay Color to Black

I'm aiming to enhance the visual appeal of my mobile menu by changing its overlay color to black on https://eric-oliver-tipq.squarespace.com/. I believe this will offer better contrast and readability. Could someone share the CSS code or steps needed to make this color adjustment for the mobile menu overlay?

You can use this code to Website > Website Tools > Custom CSS

/* Mobile menu background */
.Mobile-overlay-menu {
    background-color: #000 !important;
}