When a Rails app is generated with the --css option and the
action_text:install task is run, the Trix editor will not work as
expected. This occurs because using cssbundling-rails does not create an
application.css file, which would normally automatically require
actiontext.css.

Adding a step to append an import statement to the base CSS or SCSS
file, when one can be detected, solves the issue. In the case a base CSS
or SCSS file can't be detected, we output a warning to import the
necessary CSS file.