How To Preview Theme Edits without Being Live?

Hello, I’m starting to dive into WP, I took a few classes at school and it’s not helping.

I’m trying to make some color edits to a Theme, is there any way to preview the theme without it being live? I have not installed WP to the server yet because I want to see if I can create a better looking functioning layout than the one I have currently.

I’ve tried ThemeDreamer and it’s terrible, and not even worth the preview that it provides. Is there some kind of open source program that provides a visual to the style.css? Thanks in advance.