Flex Resourse 1

CSS-tricks is a complete guide to Flexbox layout.

Flex Resource 2

Flexbox Froggy is a tool game that helps experimenting with Flexbox properties.

Flex Resource 3

FlexBox.io is a simple free 20 video course that will help you master CSS Flexbox.

Summary

CSS flexbox provides web authors a control over how elements are positioned, aligned, and sized within their container. The benefit of FlexBox is that Flexbox simplifies the process of aligning elements. You can align items both horizontally and vertically with just a few lines of code, and without the need for complex positioning techniques.