Since Drupal 8 switched to Twig (from PHPtemplate) and a new config system Drupal themers should learn some new things. However these are good changes and I want to give you a short impression to understand why.
It is not a long course about creating a full new theme from the grond up. I'll talk about creating a sub-theme and modify the defaults provided by the parent instead.
- How to create a sub-theme?
- What are the new file formats in a Drupal 8 theme and what we use them for?
- What is new in CSS file formatting, architecture, management?
- How to use Twig in our templates?
- How to add CSS / JS (libraries) to our theme?
- How to find information about theme related changes in Drupal 8?