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You set z-index on a static element By default, every element has a position of static. z-index only works on positioned elements (relative, absolute, fixed, sticky) so if you set a z-index on an element with a static position, it won't work.
To sum up, most issues with z-index can be solved by following these two guidelines: Check that the elements have their position set and z-index numbers in the correct order. Make sure that you don't have parent elements limiting the z-index level of their children.
The maximum range is ±2147483647. In CSS code bases, you'll often see z-index values of 999, 9999 or 99999. This is a perhaps lazy way to ensure that the element is always on top. It can lead to problems down the road when multiple elements need to be on top.
Note: z-index only works on positioned elements (position: absolute, position: relative, position: fixed, or position: sticky) and flex items (elements that are direct children of display:flex elements).
Z-index is not an absolute measurement. It is possible for an element with z-index: 1000 to be behind an element with z-index: 1 - as long as the respective elements belong to different stacking contexts.
When you specify z-index, you're specifying it relative to other elements in the same stacking context, and although the CSS spec's paragraph on Z-index says a new stacking context is only created for positioned content with a z-index other than auto (meaning your entire document should be a single stacking context), you did construct a positioned span: unfortunately IE7 interprets positioned content without z-index this as a new stacking context.
In short, try adding this CSS:
#envelope-1 {position:relative; z-index:1;}
or redesign the document such that your spans don't have position:relative any longer:
<html>
<head>
<title>Z-Index IE7 Test</title>
<style type="text/css">
ul {
background-color: #f00;
z-index: 1000;
position: absolute;
width: 150px;
}
</style>
</head>
<body>
<div>
<label>Input #1:</label> <input><br>
<ul><li>item<li>item<li>item<li>item</ul>
</div>
<div>
<label>Input #2:</label> <input>
</div>
</body>
</html>
See http://www.brenelz.com/blog/2009/02/03/squish-the-internet-explorer-z-index-bug/ for a similar example of this bug. The reason giving a parent element (envelope-1 in your example) a higher z-index works is because then all children of envelope-1 (including the menu) will overlap all siblings of envelope-1 (specifically, envelope-2).
Although z-index lets you explicitly define how things overlap, even without z-index the layering order is well defined. Finally, IE6 has an additional bug that causes selectboxes and iframes to float on top of everything else.
http://www.vancelucas.com/blog/fixing-ie7-z-index-issues-with-jquery/
$(function() {
var zIndexNumber = 1000;
$('div').each(function() {
$(this).css('zIndex', zIndexNumber);
zIndexNumber -= 10;
});
});
In IE positioned elements generate a new stacking context, starting with a z-index value of 0. Therefore z-index doesn’t work correctly.
Try give the parent element a higher z-index value (can be even higher than the child’s z-index value itself) to fix the bug.
I encountered this issue, but on a large project where HTML changes had to be requested and became a whole issue, so I was looking for a pure css solution.
By placing position:relative; z-index:-1 on my main body content my header drop down content suddenly displayed above the body content in ie7 (it was already displaying without issue in all other browsers and in ie8+)
The problem with that was then this disabled all hover and click actions on all content in the element with the z-index:-1 so i went to the parent element of the whole page and gave it a position:relative; z-index:1
Which fixed the issue and retained the correct layering functionality.
Feels a bit hacky, but worked as required.
I found that I had to place a special z-index designation on div in a ie7 specific styelsheet:
div { z-index:10; }
For the z-index of unrelated divs, such as a nav, to show above the slider. I could not simply add a z-index to the slider div itself.
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