I have a standalone webpage for my portfolio and services. It's not bad, but pretty janky looking and could use a more modern look and feel. I initially used one of the themes to get it going that I think is pretty limited but am worried I'll break something if I want to switch themes.

What's the best way to go about testing a new theme/layout/etc? Can I completely copy the source code to some sort of offline testing page and dabble there, then copy/paste it back to the main page when I like what I see?