Centering a Div Both Horizontally And Vertically

While building web page layouts, you’ve probably been faced with a situation where you need to center a div both horizontally and vertically with pure CSS. There are more than a few ways to achieve this, and in this MicroTut I am going to show you my favorite involving CSS and jQuery.

1. CSS: Center a div both horizontally and vertically with CSS is a bit more tricky. You need to know the dimensions of the div beforehand.
   By positioning the element absolutely, we can detach it from its surroundings and specify its position in relation to the browser window. Offsetting the div by 50% from the left and the top part of the window, you have its upper-left corner precisely at the center of the page. The only thing we are left to do is to move the div to the left and to the top with half its width and height with a negative margin, to have it perfectly centered.
   

   .className{
   width:270px;
   height:150px;
   position:absolute;
   left:50%;
   top:50%;
   margin:-75px 0 0 -135px;
   }

2. jQuery: As mentioned earlier – the CSS method only works with divs with fixed dimensions. The functionality is inserted into a $(window).resize() statement, which is executed every time the window is resized by the user. We use outerWidth() and outerHeight(), because unlike from the regular width() and height(), they add the padding and the border width to the returned size. Lastly, we simulate a resize event to kick center the div on page load.

   $(document).ready(function(){
       
   $(window).resize(function(){
   
   $('.className').css({
   position:'absolute',
   left: ($(window).width()
     - $('.className').outerWidth())/2,
   top: ($(window).height()
     - $('.className').outerHeight())/2
   });
   
   });
   
   // To initially run the function:
   $(window).resize();
   
   });
   

http://tutorialzine.com/2010/03/centering-div-vertically-and-horizontally/