Github remote theme `invalid theme folder: _sass`

I’ve been using Jekyll on github-pages for a while to create lessons for classes I teach. I used a theme heavily derived from carpentries/styles, and it was working pretty well.

I wanted to move to a remote_theme, so I created two new repos:

The template does use the remote theme, so that’s good, but when I run bundle exec jekyll build or serve on my local copy of the template site, I get a message invalid theme folder: _sass. This message does not appear when I run the same command on the theme. I’d like to understand what’s going on.

In all honesty, I have no experience with Jekyll or Ruby outside of developing these lessons, and am just diving in.