有没有办法可以使用css3 calc在屏幕中央放置一个对话框？

Question

I am trying to use the following:

<div class="center">
  ...
</div>

CSS:

.center{
    position: absolute;
    height: 50px;
    width: 50px;
    background:red;
    top:calc(50% - 50px/2);
    left:calc(50% - 50px/2);
}

However it seems like the div is positioned not in the center of the viewport but in the center of the div that encloses it.

How can I make it so the div is positioned in the center of the screen using calc ?

Answer 1

You can use new display: flex

CSS

#overlay {
    height: 100%;
    width: 100%;
    display: -ms-flexbox;
    display: -webkit-flex;
    display: flex;
}

.dialog {
    margin: auto;
    width: 280px;
}

jsFiddle

Browser Support

Firefox, Safari 6, IE 11 (maybe 10), Opera, Chrome

Answer 2

Why don't you use:

.center {
    position: absolute;
    height: 50px;
    width: 50px;
    background: red;
    top: calc(50% - 25px);
    left: calc(50% - 25px);
}

or:

.center {
    position: absolute;
    height: 50px;
    width: 50px;
    background: red;
    margin-top: -25px;
    margin-left: -25px;
    top: 50%;
    left: 50%;
}

Answer 3

why not use the top: 0; bottom: 0; left: 0; right: 0; top: 0; bottom: 0; left: 0; right: 0; trick?

http://jsfiddle.net/3n1gm4/WpYHS/

html:

<div class="centered">
    <h1>Perfectly Centered</h1>
    <h3>This is centered top to bottom and left to right</h3>
</div>

CSS:

.centered {
    position: fixed;
    top: 0;
    left: 0;
    bottom: 0;
    right: 0;
    width: 50%; /* any width */
    height: 30%; /* any height */
    margin: auto;

    text-align: center;

    background: #deface;
}

Answer 4

I think you should use:

.center {
    float: none;
    margin-left: auto;
    margin-right: auto;
}