Understanding Display by Rachel Andrew
CSS Layout is all about boxes. We know that some boxes are blocks, and others are inline, and we can change the display type of elements by changing the value of the display property. That property holds the key to much more than this, however. It is the foundation on which all layout is built; the core of the inbuilt CSS layout system. Learning Grid Layout, or Flexbox, without understanding Display, leaves you with a wobbly foundation and more questions than answers.