Center a 'div' in the middle of the screen

问题:

I have in my page a button which when clicked displays a div (popup style) in the middle of my screen.

I am using the following CSS to center the div in the middle of the screen:

.PopupPanel
{
    border: solid 1px black;
    position: absolute;
    left: 50%;
    top: 50%;
    background-color: white;
    z-index: 100;

    height: 400px;
    margin-top: -200px;

    width: 600px;
    margin-left: -300px;
}

This CSS works fine as long as the page is not scrolled down.

But, if I place the button at the bottom of my page, when it is clicked, the div is displayed at the top, and the user has to scroll up to view the contents of the div.

I would like to know how to display the div in the middle of the screen, even when the page has been scrolled.

回答1:

Change the position attribute to fixed instead of absolute.

回答2:

Change position:absolute; to position:fixed;

回答3:

Quote: I would like to know how to display the div in the middle of the screen, whether user has scrolled up/down.

Change

position: absolute;

To

position: fixed;

---

W3C specifications for position: absolute and for position: fixed.

回答4:

I just found a new trick to center a box in the middle of the screen even if you don't have fixed dimensions. Let say you would like a box 60% width / 60% height. The way to make it centered is by creating 2 boxes: a "container" box that position left: 50% top :50%, and a "text" box inside with reverse position left: -50%; top :-50%;

It works and it's cross browser compatible.

Check out the code below, you probably get a better explaination:

<div id="message">
    <div class="container"><div class="text">
        <h2>Warning</h2>
        <p>The message</p>
        <p class="close"><a href="#">Close Window</a></p>
    </div></div>
    <div class="bg"></div>
</div>

<style type="text/css">
html, body{ min-height: 100%; }
#message{ height: 100%; left: 0; position: fixed; top: 0; width: 100%; }
#message .container{ height: 60%; left: 50%; position: absolute; top: 50%; z-index: 10; width: 60%; }
#message .container .text{ background: #fff; height: 100%; left: -50%; position: absolute; top: -50%; width: 100%; }
#message .bg{ background: rgba(0,0,0,0.5); height: 100%; left: 0; position: absolute; top: 0; width: 100%; z-index: 9; }
</style>

<script type="text/javascript">
jQuery('.close a, .bg', '#message').on('click', function(){
    jQuery('#message').fadeOut();
    return false;
});
</script>

Yay!

回答5:

Correct Method is

.PopupPanel
{
    border: solid 1px black;
    position: fixed;
    left: 50%;
    top: 50%;
    background-color: white;
    z-index: 100;
    height: 400px;
    margin-top: -200px;

    width: 600px;
    margin-left: -300px;
}