How do you edit a theme with no host?

I know this is an old topic, but the answer might be of help, still.

You can host your site on WordPress (but the URL will have the word wordpress in it), or you can host it at a hosting service like GoDaddy or HostGator or the like.

While it's possible to edit the HTML code completely offline, I personally find such editing considerably easier when you have a site and can actually see the effect of whatever you're editing.