Themes not appearing the same as "Live Preview"

When I upgraded to the latest version of WordPress, it broke my theme. By that, I mean instead of showing links in a navigation bar, it shows them in an outline format. I was using the Skeleton theme, so I figured it might be that. I installed the Decode theme after using the “Live Preview” of it, and the same issue happens there. It also happens on other themes as well.

My questions are:

Why does the “Live Preview” show the theme working properly, and then it’s broken after I activate it?
How can I fix this?

I have screenshots of this, but I don’t know how to upload them to the forum. My site is located at https://patscomputerservices.com (also it *might* be my browsers, but I don’t think so).

Thanks, and have a great day.:)
Patrick.