Creating Sub-Themes
Drupal sub theme documentation.
Resources
New community initiative: Frontend bundler
New initiative to improve frontend bundling.
Twig add to array [merge, append, push]
Examples for modifying arrays in twig.
CSS File Organization: Aggregating CSS
Documentation on how css aggregation works.
CSS architecture - for Drupal 9
Drupal css architecture documentation.
Twig dump() function uses Symfony VarDumper when available
Change record for using symfony vardumper with twig dump().
Z-indexes in Drupal 8+
List of elements in Drupal with a set z-index.
Single Directory Components Documentation
Documentation for Single Directory Components module.
Musings on HTTP/2 and Bundling
Thoughts on how HTTP2 will affect file aggregation.
New starterkit will change how you create themes in Drupal 10
Starterkit Theme announcement.