In order to include vendor assets such as CSS/JavaScript files you need to utilize Ruby on Rails Asset Pipeline. In order to implement this inclusion, you need to add file name with the require and/or @import statements in your application.js and application.css files

Here is an example of application.js file inclusions

//= require jquery
//= require jquery_ujs
//= require bootstrap
//= require turbolinks
// Vendor Files
//= require contact
//= require gmaps
//= require html5shiv
//= require jquery.prettyPhoto
//= require jquery.scrollUp.min
//= require main
//= require price-range

Here is an example of application.css.scss file inclusions

@import "bootstrap";
@import "font-awesome.min.css";
@import "prettyPhoto.css";
@import "price-range.css";
@import "animate.css";
@import "main.css";
@import "responsive.css";