Centre Div in Middle of Screen

HTML & CSS
1

hi, I have the following code, that displays a div. How do you display it so it is the centre of the screen? Similar to Yell.com

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html>
<head>
<title></title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<style>
body
{
  MARGIN: 18px;
  PADDING: 0px;
}

div
{
  WIDTH: 45.4em;
  HEIGHT: 25.5em;
  BORDER: 4px solid rgb(0,0,0);
  BACKGROUND: rgb(255,255,255);
}
</style>
</head>

<body>
<div></div>
</body>
</html>
2

Adding margin:0 auto; to the div will center it left and right (vertically).

If you are wanting to center it vertically and horizontally then things become a little trickier.

An example of that can be found Here.

An explanation of centering unknown width and height is at the bottom of that same page.

3

div
{
WIDTH: 45.4em;
HEIGHT: 25.5em;
margin: 0 auto 0 auto;
BORDER: 4px solid rgb(0,0,0);
BACKGROUND: rgb(255,255,255);
}

That works

4

Can it be centered vertically also?

5
6