Mobile sticky menu

Hello,

I have Divi and would like to make the main menu header sticky. Sorry I could not find anything working CSS (I would like to avoid any plugin…too much already)

I actually have a customized header but on mobile the menu is partly Divi (the main white band + the small black band where email adress contact is located, if you look at it) and a large black 2ndary menu from the customized menu.

Sorry I am asking in parallel the plugin team but would like to have another option from here.

Many thanks!

The page I need help with: [log in to see the link]