Install and run Discourse locally

The first step of that guide is a script to install a bunch of packages, many of which you probably already have installed, so it's worth reading the script and installing packages as needed rather than brute forcing the entire thing.

For example, the linked script will install Ruby 2.6.2 (as of this writing), but Discourse isn't locked to a specific Ruby version, so any reasonably recent version you already have installed should work just fine.

Start redis

Install discourse_theme (gem)

Run discourse_theme watch . in this directory and point it to your running copy of Discourse

The first time you run this watcher, you will be prompted to create a new theme in your copy of Discourse. On subsequent runs, the watcher will ask you to confirm that you want to modify the existing copy of the theme in Discourse (as opposed to creating another new copy).

There is a brief delay between when you save changes to these files and when those changes are synced and available in your copy of Discourse -- discourse_theme will notify you in your terminal when the sync is complete.