First, make sure you have the Polymer CLI and npm (packaged with Node.js) installed. Run npm install to install your element's dependencies, then run polymer serve to serve your element locally.
$ polymer serve
$ polymer test
Your application is already set up to be tested via web-component-tester. Run polymer test to run your application's test suite locally.
The platform use granite-bootstrap, a wrapping of Bootstrap CSS as Polymer shared styles modules (i.e. inside tags).