Just fork the repo and adjust the _config.yml to use with Github Pages and your page is done.
Note: If you want to use this theme in a subfolder, then you need to create a gh-pages branch in your repo.
You can also create an empty repo, add index.html and archive.html files, which can be empty but need to contain a front matter, and add add this to your _config.yml:
remote_theme: niklasbuschmann/contrast
plugins:
- jekyll-remote-theme- supports dark mode in macOS Mojave
- MathJax support
- included archive page
- supports pagination
- feed generation
- responsive
- syntax highlighting
- supports comments via disqus or isso
