This tutorial is about setting the Div height to 100% of the body or the window of the browser. There are two different pure CSS approaches shown here....

To center a div horizontally margin: 0 auto; is enough but for an absolutely centered div both vertically and horizontally requires few more things...

To center a div horizontally in a div you need just one property of CSS i.e. margin. To center it you need to give width to the outer or parent div and for inner or child div to need to set margin....