Why Doesn't My Z-Index Work in Internet Explorer 7?

IE7 Z-Index Layering Issues: A Stacking Context Dilemma

Z-index, a CSS property, allows for the layering of HTML elements on a webpage. However, Internet Explorer 7 (IE7) exhibits an unusual behavior with z-index layering.

In this scenario, the developer set a high z-index (1000) on a UL list, intending it to overlap a div. However, the div remained visible in front of the UL. The issue lies in IE7's interpretation of stacking contexts.

Stacking contexts are independent layers created in the browser's rendering process, where z-index values are evaluated separately within each context. IE7 interprets positioned elements without explicit z-index as creating new stacking contexts, even though the CSS specification states otherwise.

To resolve the issue, add an explicit z-index value to the positioned span element:

#envelope-1 {
    position: relative;
    z-index: 1;
}

This will create a new stacking context for the span and ensure that the UL list overlaps the div as intended.

Alternatively, redesign the document to avoid using position:relative on the spans, as this forces the creation of separate stacking contexts:

<div>
    <label>Input #1:</label> <input>
    <ul>
        <li>item</li>
        <li>item</li>
        <li>item</li>
        <li>item</li>
    </ul>
</div>

By understanding the concept of stacking contexts and their interpretation in IE7, developers can effectively control the layering of elements, even when facing browser-specific inconsistencies.

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