You will need to create some custom CSS to override what the theme has by default which is this:
.primary-navigation li,
.site-navigation li {
margin-bottom: 6px;
font-family: "Open Sans",sans-serif;
font-weight: 300;
font-size: 1.438rem;
line-height: 1.4;
}
All you need to do is create a new version like this:
.primary-navigation li,
.site-navigation li {
font-size: 1.438rem;
}
Change the font-size of 1.438rem to your own preference. For a reference, use this online conversion tool https://www.pxtoem.com to see how many pixels (px) 1.438rem is (which is 23px). I recommend keeping the size as rem units though. So if you want a smaller font size, try something like 1.25rem (which is 20px).
If you also need your submenus to be a bit smaller, this CSS will do that:
.primary-navigation .sub-menu li {
font-size: 1.063rem;
}
Again, just change the 1.063rem to your preference.
IMPORTANT: To make any kind of changes to a theme (any theme), it’s recommended to use a child theme method. However, if you just need to modify CSS code only, then you have a couple options:
1. Jetpack (if you have it installed) has a Edit CSS module (feature) that you can use to add your custom CSS to.
2. Simple Custom CSS is a plugin that does a similar function, it lets you add your own custom CSS.
