Sorry for late reply…the WordPress site is changing their forums and the rSS feeds are not working yet, so I can get notified of posts.
Anyway, it looks like your image is broken. But if you want the menu links to be bold, you will need to do some custom CSS. If you are using a child theme, you can do this in the style.css file for it, or if you are using Jetpack, you can use its Custom CSS feature, otherwise, use a plugin like Simple Custom CSS.
You will want to do this:
.main-navigation {
font-weight: 600;
}
or you can go bolder with:
.main-navigation {
font-weight: 700;
}
Making the menu items bolder will help make the colour appear darker. If you want to manage the size of the menu font, you can do that from the customizer by going to Appearance >> Customize >> Typography Options
