While Drupal 8 ships with some improvements to its default CSS and JavaScript libraries, we will generally find ourselves wishing to add additional third-party libraries that can enhance the function and feel of our website. In our case, we have decided to add Twitter Bootstrap (http://getbootstrap.com), which provides us with a responsive CSS framework and JavaScript library that utilizes a component-based approach to theming.

The process involves three steps:

1. First is downloading or installing the assets that make up the framework or library.
2. Second is adding library entries that point to our assets.
3. Finally, we will need to add a library reference to our twiggy.info.yml file.