Webkit-Transform Overwrites Z-Index Ordering in Chrome 13

z-index is canceled by setting transform(rotate)

Let's walk through what is occurring. To start, note that z-index on positioned elements and transform by itself create new "stacking contexts" on elements. Here's what's going on:

Your .test element has transform set to something other than none, which gives it its own stacking context.

You then add a .test:after pseudo-element, which is a child of .test. This child has z-index: -1, setting the stack level of .test:after within the stacking context of .test Setting z-index: -1 on .test:after does not place it behind .test because z-index only has meaning within a given stacking context.

When you remove -webkit-transform from .test it removes its stacking context, causing .test and .test:after to share a stacking context (that of <html>) and making .test:after go behind .test. Note that after removing .test's -webkit-transform rule you can, once again, give it its own stacking context by setting a new z-index rule (any value) on .test (again, because it is positioned)!

So how do we solve your problem?

To get z-index working the way you expect, make sure that .test and .test:after share the same stacking context. The problem is that you want .test rotated with transform, but to do so means creating its own stacking context. Fortunately, placing .test in a wrapping container and rotating that will still allow its children to share a stacking context while also rotating both.

Here's what you started with: http://jsfiddle.net/fH64Q/
And here's a way you can get around the stacking-contexts and keep
the rotation (note that the shadow gets a bit cut off because of .test's white background):

.wrapper {

    -webkit-transform: rotate(10deg);

}

.test {

       width: 150px;

       height: 40px;

       margin: 30px;

       line-height: 40px;

       position: relative;

       background: white;

}

.test:after {

       width: 100px;

       height: 35px;

       content: "";

       position: absolute;

       top: 0;

       right: 2px;

       -webkit-box-shadow: 0 5px 5px #999; /* Safari and Chrome */

       -webkit-transform: rotate(3deg); /* Safari and Chrome */

       transform: rotate(3deg);

       z-index: -1;

}

<div class="wrapper">

    <div class="test">z-index is canceled.</div>

</div>

Strange looking words using webkit transform rotate in chrome

Chrome uses Windows GDI for text drawing on Windows. I'm guessing that to rotate, it will draw the horizontal text to a bitmap in memory and then rotate it and render it to the screen. Could be an issue with preserving the font smoothing or maybe font hinting is being done assuming the horizontal orientation then the transformation is applied; resulting in the pixel distortion. You may also be interested in subpixel rendering.

Here's a blog comparing subpixel rendering in chrome and firefox. This is an older article about Firefox's font rendering.

Webkit-Transform Overwrites Z-Index Ordering in Chrome 13

z-index is canceled by setting transform(rotate)

Strange looking words using webkit transform rotate in chrome

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