z-index IE8 bug on generated content with :after

问题

This is a known error in IE8, look at the last bug here:
http://nicolasgallagher.com/css-typography-experiment/demo/bugs.html

Now, playing a bit with a simple example I found this (test it using IE8):
http://jsfiddle.net/AjCPM/

<div id="target">
   <div>div</div>
</div>


#target {
    position: relative;
    width: 200px;
    height: 200px;
    z-index: 1;
}
#target>div{
    background: red; width: 200px; height: 200px;  
    position: relative;
    z-index: 0;
}
#target:before {
    top: 0; left: 10%; width: 100%; height: 100%; background: cyan;
    content: "after";
    position: absolute;
    z-index: 10;
}

IE8 renders the cyan rectangle (the :after) below the red rectangle, even when it has lower z-index.
And now the tricky part:
change the z-index for #target>div from 0 to -1 and voilá ! it's solved !

So I solved my problem now using a lot of z-index: -1;
But I don't feel safe with this.

Do you know a better solution?

I'm using the :after pseudoelement because I have a list of products, and I want to add an image to the the item when it has the class 'sold' for example.
I can create in the server or with JS a new html element for that, but I think using :after is the correct semantic solution.
The problem is that I'm a bit paranoid about the :after pseudoelement now, do you think is better to avoid it?

回答1:

To answer your last question first, as long as you don't need to support any browsers that completely lack support for generated content (http://caniuse.com/#feat=css-gencontent) then you shouldn't need to avoid it. However, since you note that this is a known bug, you should be careful about it.

In this specific example, I can think of three different ways to work around the bug. Whether these are useful to you depends on your actual use case.

Use :after instead of :before and remove positioning from the child div: http://jsfiddle.net/AjCPM/24/

#target {
    position: relative;
    width: 200px;
    height: 200px;
    z-index: 1;
}

#target>div{
    background: red;
    width: 200px;
    height: 200px;
}

#target:after {
    content: "after";
    position: absolute;
    top: 0;
    left: 10%;
    width: 100%;
    height: 100%;
    background: cyan;
    z-index: 10;
}

Add the after to the child div instead of the parent: http://jsfiddle.net/AjCPM/26/

#target {
    position: relative;
    width: 200px;
    height: 200px;
    z-index: 1;
}

#target>div{
    position: relative;
    background: red;
    width: 200px;
    height: 200px;
    z-index: 0;
}

#target>div:before{
    content: "after";
    position: absolute;
    top: 0;
    left: 10%;
    width: 100%;
    height: 100%;
    background: cyan;
    z-index: 10;
}

Use a wrapping element (usually because you already have one) to apply the base styling to: http://jsfiddle.net/AjCPM/29/

 <div id="target">
     <div id="wrap">
         <div>div</div>
     </div>
 </div>

#target {
    position: relative;
    width: 200px;
    height: 200px;
    z-index: 1;
}

#wrap>div{
    position: relative;
    background: red;
    width: 200px;
    height: 200px;
    z-index: 0;
}

#wrap>div:before{
    content: "after";
    position: absolute;
    top: 0;
    left: 10%;
    width: 100%;
    height: 100%;
    background: cyan;
    z-index: 10;
}

Basically, when faced with a difference in interpretation between browsers like this, your best bet is to try to rearrange your approach to find something that works cross-browser.

回答2:

No need to set z-indexes, just make sure you use :after instead of :before (demo):

#target {
    position: relative;
    width: 200px;
    height: 200px;
}
#target>div{
    background: red;
    width: 200px;
    height: 200px;
}
#target:after {
    content: "after";
    position: absolute;
    top: 0;
    left: 10%;
    width: 100%;
    height: 100%;
    background: cyan;
}

Since the generated content comes after #target, it will naturally be stacked above.

BTW Whether a product is "sold" or not is semantic information, and so the correct semantic solution would be to include it in the HTML, rather than adding the image through CSS.

回答3:

A quick note on the :before and :after selectors in IE8: for them to work you need to declare a DOCTYPE. See this W3Schools page. I am guessing you have already done this though.

See the answer to this question if you haven't already (I think you probably have).

Basically, the bottom line is that it's a bug. Your solution of using a z-index of -1 is not ideal, but then again NO work around for the bug is going to be ideal. I don't think that using a z-index of -1 is something to be overly concerned about, unless it causes issues in your layout. If you are very concerned, then why don't you ONLY target IE8 w/ the fix. For example, you could use a conditional comment like so:

<!--[if IE 8]>
<style>
#target>div{
  z-index:-1;
}
</style>
<![endif]-->

Behaviors like the one you are experiencing is one of the reasons many developers despise IE. In many cases, including this one, there is no perfect solution. You could:

stop using the :before and :after selectors & adjust your HTML/CSS to something that is IE8-friendly.
Use conditional comments or JavaScript to issue a fix that specifically targets IE8
Keep hacking and try to find another HTML/CSS combo that works -- but chances are it won't be any more ideal than your negative z-index solution.

Unfortunately, in many cases there is no such thing as a "semantically correct" cross-browser website.

My two cents is to create an IE8 stylesheet and use the conditional comment I displayed above to load the stylesheet. Within the stylesheet, use the z-index: -1 solution you came up with. Many websites use IE-targeted stylesheets.

回答4:

I use a different method to solve this problem:

The HTML for each product contains a "sold out" banner that can be positioned over the main image. By default the CSS hides this element. If the wrapping "product" DIV contains a class of "soldOut" the CSS will override the default declaration and display the banner.

<div class="product soldOut">                                   
    ... product html ...
    <div class="soldOutBanner"></div>    
</div>

CSS:

.soldOutBanner {
     display:none
}

.soldOut .soldOutBanner {
    display:block; 
    width:133px;
    height:130px;
    position:absolute;
    top:0px;
    right:0px;
    z-index:10;
    background-image:url(../SoldOut.png);
}

来源：https://stackoverflow.com/questions/8828767/z-index-ie8-bug-on-generated-content-with-after

标签

css

internet-explorer-8

z-index

pseudo-element