How to position a table at the center of div horizontally & vertically

Centering is one of the biggest issues in CSS. However, some tricks exist:

To center your table horizontally, you can set left and right margin to auto:

<style>
  #test {
    width:100%;
    height:100%;
  }
  table {
    margin: 0 auto; /* or margin: 0 auto 0 auto */
  }
</style>

To center it vertically, the only way is to use javascript:

var tableMarginTop = Math.round( (testHeight - tableHeight) / 2 );
$('table').css('margin-top', tableMarginTop) # with jQuery
$$('table')[0].setStyle('margin-top', tableMarginTop) # with Mootools

No vertical-align:middle is possible as a table is a block and not an inline element.

Edit

Here is a website that sums up CSS centering solutions: http://howtocenterincss.com/