Menu not showing up font size issue

Hello ??
I have two questions about my theme (my website is https://www.adventureswithluda.com)

There should be a menu bar on the top (you can see it if you hover over the top, or if you scroll a little– there should be white text). How can I get it to show up again? – for example, maybe change the text to black.

Also, how can I change the size of my font on every page (not just on one post)? I think it might be too small right now.

Thank you! ??