Page API: Some of the API not working properly

Currently im using ERPNext-15
In some of the Page API like

let $btn = page.set_primary_action('New', () => create_new(), 'octicon octicon-plus')

The icon octicon octicon-plus is not working properly. please help some one i want to add the icon.

I have some doubts in ERPNext front end.

  1. Is ERPNext using the Bootstrap.
  2. If yes can I use the all the BootStrap classess

Icon Not there.