I just added some custom CSS and it seems to be working. It could probably use a few tweeks.
.header-nav-list {
display: none;
}
.header-display-desktop .showOnMobile {
display: flex;
}
.header .header-burger {
margin-right: 0;
align-items: flex-end;
justify-content: flex-end;
flex: 0 0 50px;
width: 50px;
}
.header-burger {
display: flex;
}
.header--menu-open .header-menu {
opacity: 1;
visibility: visible;
}