How to change the top menu

I’d like to edit the CSS so that the very top menu is not affected by screensizes (I want it to look the way it does on large screens – ie I don’t want a drop-down there). I spent a long time in the CSS and I can’t figure it out. What do I need to display:none and remove display:none from, please?

Thanks. I like the theme so far, although I’m just setting it up.