I have a GitHub Pages site that I generated by creating a repository and choosing a theme on GitHub. While the site is technically built using Jekyll, it has no gemfile, and the _config.yml is very concise:
theme: jekyll-theme-dinky
title: "<site name>"
In contrast, proper Jekyll sites created with jekyll new . have proper gemfile and gemfile.lock files, and a verbose _config.yml. Pardon my general ignorance with Jekyll and Ruby, but I assume these are necessary for Jekyll to build the site locally.
Running jekyll serve on a local clone of my site doesn't build the site properly. Yet GitHub's own pipeline can.
The question: Is there a way to locally build and preview my site without adding a gemfile/gemfile.lock and changing _config.yml? I.e. do exactly what GitHub's pipeline does, just on my computer.