This site depends on the private repository mythic-brand as a Git submodule. See the README there for more information.
To install, alter the usual clone command to git clone --recurse-submodules. However, if you have already cloned this repository, and the "brand" submodule folder is empty, you will need to run git submodule init followed by git submodule update instead.
Further information on using submodules can be found in the Git docs
For development, use npm start and for a production build use npm run build. When in development, Eleventy and Browser Sync will watch for changes and auto-update the page in the browser.