The Shapes of CSS
CSS is capable of making all sorts of shapes. Squares and rectangles are easy, as they are the natural shapes of the web.
CSS
A Complete Guide to Flexbox
A comprehensive guide to CSS flexbox layout. This complete guide explains everything about flexbox, focusing on all the different possible properties for the parent element (the flex container) and the child elements (the flex items). It also includes history, demos, patterns, and a browser support chart.