Burger menu drop down

Site URL: https://maroon-iris-8gg6.squarespace.com/

I created a burger menu in CSS, but I want to change the background color of the menu that pops up to a beige/sand color. How do I do that?

Also I would like to add a link to my LinkedIn and Instagram account at the buttom of the menu - is that possible?

The first screenshot shows how the menu looks now. The second shows which colour I want the background to be and where I want to place the social media links

Add to Design > Custom CSS

better-burger.is-open {
    background-color: #f1f2;
}