Change Menu Bar Opacity

hey,

i want to change the opacity of the menu bar on my site from transparent to opaque. I tried adding:

.main-navigation {
opacity: 1.0;

to the CSS but it made no difference. you can see the transparent bar as is on my site fluorescent-beige.com

let me know if you know how to fix this!

https://wordpress.org/themes/book-lite/