Learn CSS Layouts
If you’re struggling to get down the finer details of putting together a CSS layout, check out this thorough tutorial by Mikito Takada, walking you through each and every major concept in CSS layouts, including lots of examples that illustrate each concept.
The tutorial is divided into five chapters that include box positioning, box sizing, and flexbox. This tutorial should prove to be a super-valuable resource!
Read the tutorial here: http://book.mixu.net/css