Problem Changing Theme Font Size For One Menu!

I've just set up a new website (crazyoddweird.everythingprint3d.com) and after HOURS of searching, I found the right theme for what I needed. I've got it pretty much set up how I want it. Except one thing: the menu font is too small.

I've done a few searches on WA to find blogs/tutorials on how to change the font and I found one that looked promising:

https://my.wealthyaffiliate.com/training/change-font-size-in-wordpress-omg-code

I went through the steps of the video, as follows:

1. Go to the Editor in WP, to the Stylesheet:

2. Ctrl-F to find the "font-size" phrase in the stylesheet at the section you want to change. In my case, I want to change the size of the menu font

Now the image on the screen shows the font-size highlighted. This is the only one in the "small menu" section, and this is the only menu section with a "font-size" in it that could be found in the stylesheet.

I've already changed the font size in this snapshot, from 2 to 10. I clicked "Update File" and refreshed the already open page I had for my site.

But nothing changed!

The tutorial I used above made total sense and I believe I've followed the steps as stated. So why does the computer say "NO!"?

The name of the theme I'm usng is BirdSITE.

If anyone in WA has any idea where I go from here, please let me know. It's very frustrating.

Looking forward to your help.

Cheers,

Scott