Awesome Flexbox Resources
Article by @Chris Coyier
https://css-tricks.com/snippets/css/a-guide-to-flexbox/
Article by @Sara Soueidan
http://tympanus.net/codrops/css_reference/flexbox/
Article by @Dimitar Stojanov
https://scotch.io/tutorials/a-visual-guide-to-css3-flexbox-properties
Learning material for flexbox(20 videos)
http://flexbox.io/
Solved by Flexbox by @philipwalton
http://philipwalton.github.io/solved-by-flexbox/
W3schools
http://www.w3schools.com/css/css3_flexbox.asp
Flexbox support in browsers
http://caniuse.com/#feat=flexbox
http://html5please.com/#flexbox
MDN
https://developer.mozilla.org/en-US/docs/Web/CSS/CSS_Flexible_Box_Layout