Adjusting height of top navbar

I’ve added our logo to the primary navbar at the top. I need to increase the height of the navbar to accommodate the logo, which I’m using as a background-image. If I specify the height of any of the tags used in that structure, I will get the first screen to look fine, but that nice feature where the navbar converts into a fixed navbar at the top as we scroll down vasnishes. I’ve run around in circles with this for awhile.

I’d like to understand how this effect is working in general, and why specifying height has this effect.

Here’s the site:

https://lkc1.club

The fixed scrolling navbar is working and looking fine now. If I try to get the initial screen of it, however, to be the proper height, I’ll lose the fixed navbar.

Thanks!