CSS: Vertically align div when no fixed size of the div is known

Question

How do I align a <div> which contains an image (or flash) vertically with CSS. Height and width are dynamic.

Answer 1

This is a pure CSS2 solution for horizontally and vertically centering without known sizes of either container nor child. No hacks are involved. I discovered it for this answer and I also demonstrated it in this answer.

The solution is based on vertical-align: middle in conjunction with line-height: 0, which parent has a fixed line-height.

The HTML:

<span id="center">
    <span id="wrap">
        <img src="http://lorempixum.com/300/250/abstract" alt="" />
    </span>
</span>

And the CSS:

html,
body {
    height: 100%;
    width: 100%;
    padding: 0;
    margin: 0;
    overflow: hidden;
}
#center {
    position: relative;
    display: block;
    top: 50%;
    margin-top: -1000px;
    height: 2000px;
    text-align: center;
    line-height: 2000px;
}    
#wrap {
    line-height: 0;
}
#wrap img {
    vertical-align: middle;
}

Tested on Win7 in IE8, IE9, Opera 11.51, Safari 5.0.5, FF 6.0, Chrome 13.0.

The only caveat is IE7, for which the two innermost elements have to declared at one line, as demonstrated in this fiddle:

<span id="center">
    <span id="wrap"><img src="http://lorempixum.com/300/250/abstract" alt="" /></span>
</span>

Note that the span's are also required for IE7. In every other browser, the span's may be div's.