create a button in the header of the mobile menu in the middle of the logo and the menu accordion

It looks like the following code, the z-index works differently on mobile:

#masthead:not(.menu-absolute){
z-index: 2000;
position: relative;
}

I’d suggest you put the HTML for that button in the same line as the logo and mobile menu then hide/show it when you need to.

It would placed under this HTML

<div id="logo-container-mobile" class="col-lg-0 logo-container middle">