Use Tailwind CSS, Bootstrap, Bulma, PostCSS, or Dart Sass to bundle and process
your CSS, then deliver it via the asset pipeline in Rails. This gem provides
installers to get you going with the bundler of your choice in a new Rails
application, and a convention to use app/assets/builds to hold your bundled
output as artifacts that are not checked into source control (the installer adds
this directory to .gitignore by default).

You develop using this approach by running the bundler in watch mode in a
terminal with yarn build:css --watch (and your Rails server in another, if
you're not using something like puma-dev). You can also use ./bin/dev, which
will start both the Rails server and the CSS build watcher (along with a JS
build watcher, if you're also using jsbundling-rails).