What is the easiest method for vertical+horizontal centering of a div in the window?

Question

Given a div with known dimensions, say width: 300px; height: 200px, what is the easiest method to place it in the middle of the screen both vertically and horizontally ? Example here

I'm interested in latest Firefox (no need for IE hacks).

CSS only please, no Javascript.

Answer 1

Position it 50% from the window/parent container and use a negative margin size that's half of the elements width/height :)

position: absolute; // or fixed if you don't want it scrolling with the page.
width: 300px;
height: 200px;
left: 50%;
top: 50%;
margin-left: -150px;
margin-top: -100px;

You might need to set height: 100%, on both the body and html

html, body {
    height: 100%;
}

Edit: Here's a working example .

Answer 2

Without supporting IE, this is actually pretty easy to achieve using display: table and display: table-cell.

Here's an update to your HTML:

<div id='my_div'>
    <div class="centered">this is vertically centered</div>
</div>

CSS:

body, html
{
    height: 100%;
}
body
{
    margin: 0;
    padding: 0;
    border: 1px solid blue;
}
#my_div
{
    width: 300px;
    border: 1px solid red;
    margin-left: auto;
    margin-right: auto;
    height: 100%;
    display: table;
    overflow: hidden;
}
.centered
{
    display: table-cell;
    vertical-align: middle;
    text-align: center;
}

And to preview: http://jsfiddle.net/we8BE/