“CSS”
CSS Dig
Analyze your CSS in a new way. Consolidate, refactor, and gawk at the 37 shades of blue your site somehow ended up with
Image Effects with CSS
Controlling color with Sass color functions
CSS3 Patterns Gallery
Lea Verou writes about CSS3 patterns
CSS Display Module Level 3
Flexbox Patterns
Build awesome user interfaces with CSS flexbox. Examples and source code included.
Understanding Flexbox
Everything you need to know
The Ultimate Guide to Flexbox
— Learning Through Examples