I just looked at your Kookaburra album linked above on my desktop (I’ve been on my ipad all morning)>
The desktop navigation items are bold and the font size is 37px, making the navigation menu unwieldy on desktop monitors.
I’m able to change colors in my mobile navigation. To remove the borders, change the border color to march the background color
On your site, when I shrink the browser to below the breakpoint, the vertical navigation just appears without me needing to click on the mobil menu icon. Not sure why that’s happening.
Admittedly, I’m not as familiar with Kookaburra as I am with Pangolin.
The main reasons I’ve found for changes not showing as expected: Template cache. Sometimes you need to clear template cache. Working on the wrong template. I’ve done this more often than I care to admit. Custom css taking priority over template control settings
I don’t see any settings for changing font-weight for mobile menu items.
This may be by design so that navigation menu items don’t take up too much space on mobile devices.