Drupal 8 revolutionizes the theming experience with many significant improvements to make theming easier, more future proof, and give themers the flexibility and control they've never had before. One of those major improvements is to the library management system, for managing CSS and JavaScript files. In this session we will cover how to create and control libraries (primarily from a theme.) This will include SMACSS categorization for CSS files, how to conditionally attach libraries, dependencies, manipulating libraries that come from anywhere else in the site (core, modules, or base themes,) and targeting individual files for removal or replacement. All without needing a single line of PHP.