Neocities.org
How do some people create navbars with buttons that change only one certain main (non-iframe) div? I can't properly explain it but I've seen some sites like that.
Edit: FOUND OUT THAT I'M REFERRING TO CSS TABS! I did get some external help from Discord
Javascript. I have a site that uses switch-case to replace the html in a document, and some people write the navigation with a script to appear on all pages.