Drupal 8 introduced a new, high-level principle of managing assets using a libraries configuration file that can be loaded globally or on a per page basis. This concept helps to improve frontend performance as well as ensure that any dependencies that an asset needs is loaded properly. One advantage of this is that jQuery no longer loads on every page as it did in the previous versions of Drupal.

The concept of a *.libraries.yml configuration file also means that the style sheets and scripts properties that we may have been familiar with in Drupal 7 no longer exist. Instead, the process to manage assets includes saving any CSS or JS files to our theme's CSS or JS folder and then defining a library file that references the less we want to use in our theme.