like last time, you must know the width and height of the element you want to center. Then set the childs display property to absolute, top to 50, and left to 50.
At this time (2014), a good way to center blocks vertically without using absolute positioning (which may cause overlapping text) is still under discussion. But if you know that overlapping text will not be a problem in your document, you can use the transform property to center an absolutely positioned element.
css How to align to center? Stack Overflow
If you dont specify the width attribute, a div will always take up 100 of its parents width - unless floating or positioned absolutely.
Center definition is - the point around which a circle or sphere is described broadly a point that is related to a geometrical figure in such a way that for any point on the figure there is another point on the figure such that a straight line joining the two points is bisected by the original point called also center of symmetry.