Sue, there are a quite a few options here, but this is a simple demo:
https://initiostar.co.uk/demo/simpleHeader/ and here is the XAR:
Simple Navbar.xar
One option is to add a mobile menu layer as a popup and to link your 'hamburger' icon to it. In the example these are just text links on the mobile menu layer, but open up the XAR and it will give you an idea. In the example, you will see it uses scale-to-fit-width and transitions from a desktop, through tablet to mobile.
There are countless tweaks, mods and ideas for mobile menus; just depends on what you want to achieve.
Gary
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