Writing CSS is easy. Writing CSS that can scale and can be easily maintained is not.
At DrupalCamp Atlanta 2015, I presented a session on how to achieve next-level CSS. My presentation focused on techniques and best practices for writing scalable, maintainable CSS.
Check out this video of my session "Leveling up CSS with SMACSS and BEM" that explores:
Using SMACSS and BEM with Drupal
Lessons learned (the hard way)
Theme architecture
Refactoring current or inherited projects to be less awful
Slides ( PDF ): https://goo.gl/QucGJB
Just the links: https://goo.gl/QDTPl1
Additional Resources
Techniques for Successfully Co-Theming with Others | Blog
Cleaner and Semantic Markup with Drupal's Views | Blog
Converting a Drupal 7 Theme from CSS to SASS | Blog
