A Complete Guide to Flexbox
“The Flexbox Layout (Flexible Box) module (currently a W3C Last Call Working Draft) aims at providing a more efficient way to lay out, align and distribute space among items in a container, even when their size is unknown and/or dynamic (thus the word ‘flex’).”
Mozilla Developer Network
“The Mozilla Developer Network (MDN) provides information about Open Web technologies including HTML, CSS, and APIs for both Web sites and HTML5 Apps. It also documents Mozilla products, like Firefox OS.”
Can I use… Support tables for HTML5, CSS3, etc
“‘Can I use’ provides up-to-date browser support tables for support of front-end web technologies on desktop and mobile web browsers.”