Unicon Theme (Mobile) Top Navigation / Hamburger Menu Icon

Hello support team,
I have the following additional problems:
1. The top navigation is not displayed on mobile devices!
2. The main menu (hamburger menu) is also not displayed.

– See images: https://imgur.com/a/PRsPyAG

3. I have already inserted the following into the .css:
.mobile-navigation-btn i{
font-family: FontAwesome !important;
}

#topbar{
position: sticky !important; top: 0px;
}

#header{
position: sticky !important; top: 40px;
}

but without success.

I would be very grateful for your help.

Ticket