This is a demo Rails app, so just run the usual Rails commands to get up and running.
Clone the repo, then run bundle and rails s to start the server.
Check app/views/welcome/index.html.erb — the code is commented.
Essentially we have a list of view partials under app/views/components and we want to load the best available version, given a constraint such as ~> 1.1.2 (following the Gemfile notation).
If it exists, we render it, otherwise we rescue the exception and display an error on the page.