Why Does My Div Stacking Order Behave Differently in IE6 and 7?

Internet Explorer 6 and 7 Z-Index Issue

Problem:
In a web page with two divs, div#sign-post should appear above div#bottom, but this only occurs in browsers other than Internet Explorer (IE) 6 and 7. Additionally, IE6 displays an extra 198 pixels at the top of div#bottom.

Solution:

Understanding Z-Index in IE6/7

In most browsers, the z-index property allows elements to be stacked above or below others based on their assigned values. However, in IE6 and 7, positioned elements create new stacking contexts regardless of z-index values.

The Problem

In this case, div#sign-post has a higher z-index than div#bottom, but IE6/7 compare the stacking contexts of their parents, which in IE are created by the positioned elements themselves. Since neither div#sign-post nor div#bottom have explicitly set z-index values, document order determines their stacking, causing div#bottom to appear on top.

Workaround:

To resolve this issue, it is necessary to assign z-index values to the positioned ancestors of the affected elements.

1. Identify the positioned ancestors that create the stacking contexts.
2. Use JavaScript or CSS to assign a high z-index to these ancestors, forcing the desired stacking order.

For example, if div#parent contains div#sign-post, assign a z-index of 1000 to div#parent to place it above div#bottom.

Additional IE6 Issue

The extra 198 pixels at the top of div#bottom in IE6 is due to an internal calculation of its default margin. This issue can be resolved by explicitly setting the margin of div#bottom to 0px.

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