Doubt about building the server, the web, github, etc...

Hey people!!
I'll get to the point and be direct.
In order to change some of the css, icons etc of the legacy website, do I have to build the server first?
I think I'm confusing needing to have both with being to modify both.
For now is to work in local and in the future make same in my VPS.
Cheers!

If you're just changing the web app, of course you don't need to build the server.

Thanks for your time and excuse me my confussion.
Cheers!