The aim in this case is to centre the page or a section of a page (a div) but not centring the text or images within the page or block.
So you can’t use text-align: center in your CSS as this will centre text.
The solution is to use either in the CSS for the DIV being centred after the width property:
margin-left: auto ;
margin-right: auto ;
or you could try:
margin: 10px auto 10px auto;
(the syntax being margin: top right bottom left;)
The article, How to Centre a DIV Block Using CSS by Christopher Heng shows very clearly how to do this in detail.