To simplify the app build process, and also make it easier for us to open source a lot of the project without Microsoft-specific assets and content, the site pulls its static assets (favicon, graphics, client scripts) from an NPM package.
Inside the app's package.json, a property can be set, static-site-assets-package-name,
pointing to the name of an NPM package (public or private) that contains those assets.
By default, this project contains a default-assets-package sub-folder NPM package
with more generic Bootstrap content, Grunt build scripts, etc. It is used if this variable
is not defined in the package JSON. Unfortunately you need to separately
npm install and grunt to use it, or just point it at your own set of
CSS files and other assets. Sorry, its not pretty.