Flexbox Cheatsheet
I always viewed <a href="https://css-tricks.com/snippets/css/a-guide-to-flexbox/" rel="nofollow">https://css-tricks.com/snippets/css/a-guide-to-flexbox/</a> as the definitive flexbox resource, and <a href="https://github.com/philipwalton/flexbugs" rel="nofollow">https://github.com/philipwalton/flexbugs</a> for browser specific issues