css - How to position a div in the middle of the screen when the page is bigger than the screen

Question

Hi I'm using something similiar to the following to get a div positioned in the middle of the screen:

<style type="text/css"> 
#mydiv {
    position:absolute;
    top: 50%;
    left: 50%;
    width:30em;
    height:18em;
    margin-top: -9em; /*set to a negative number 1/2 of your height*/
    margin-left: -15em; /*set to a negative number 1/2 of your width*/
    border: 1px solid #ccc;
    background-color: #f3f3f3;
}

</style>


<div id="mydiv">Test Div</div>

However the problem with this is it positions the item in the middle of the page not the screen. So if the page is a few screen high and I'm at the top of the page (the top part of the part is displayed on the screen) when I make the div appear it's not even on the screen. You have to scroll down to view it.

Can someone please tell me how you'd make it appear in the middle of the screen?

Answer 1

just add position:fixed and it will keep it in view even if you scroll down. see it at http://jsfiddle.net/XEUbc/1/

#mydiv {
    position:fixed;
    top: 50%;
    left: 50%;
    width:30em;
    height:18em;
    margin-top: -9em; /*set to a negative number 1/2 of your height*/
    margin-left: -15em; /*set to a negative number 1/2 of your width*/
    border: 1px solid #ccc;
    background-color: #f3f3f3;
}