- Layout vs style
- https://css-tricks.com/snippets/css/a-guide-to-flexbox/
- https://scotch.io/tutorials/a-visual-guide-to-css3-flexbox-properties
- http://flexbox.io (video tutorials)
- http://www.sketchingwithcss.com/flexbox/ (video-html tutorial, what?)
- http://flexboxfroggy.com/ (a game!)