Modify appearance of the mobile menu

Hello!

This is my first message in this forum after longtime search and I'm starting with a simple question :

• How to edit the appearance of the mobile menu?

I'm talking about the full screen popup that appears when you click on the hamburger.

How to change the wallpaper color? It is gray in my site and I don't understand what the color corresponds to, when I look in the style of the site it is not present anywhere.

• How to change the style of menu items?

Can we center the elements or align them on one side?
Can we change the menu colors?

I don't understand whats happening because I see tutorials but they seem to correspond to old versions of Squarespace which had options which seem to have disappeared.

Thanks in advance !

THANKS. That works. My problem is that I can't quite activate the Style Theme when I want it. While I thought I was validating the activation of a Theme, it is in fact another one that is active. The interface is really not easy to understand for me (Worpress user)