For vertically align content in div you must set display property to table to your parent div and table-cell to child div. you can vertically align content according to your need i.e Top, Middle, Bottom.

CSS

#parent-div
{
 width:300px;
 height:300px;
 background:#ccc;
 display:table;
}
#child-div
{
 display:table-cell;
 vertical-align:middle;
 text-align:center;
}

HTML

 
This is a content vertically align in div.

Download File Used in this example View Live Demo

To Centring Absolute Div on page you must know height and width of div.

Css Code

.mydiv
{
position:absolute;
height:500px;
width:500px;
top:50%;
left:50%;
margin-top:-250px;
margin-left:-250px;
}

HTML CODE

My Centered Div Content