When using IE, you cannot put an absolutely positioned div over a select input element. That's because the select element is considered an ActiveX object and is on top of every HTML element in the page.

I already saw people hiding selects when opening a popup div, that leads to pretty bad user experience having controls disappearing.

FogBugz actually had a pretty smart solution (before v6) of turning every select into text boxes when a popup was displayed. This solved the bug and tricked the user eye but the behavior was not perfect.

Another solution is in FogBugz 6 where they no more use the select element and recoded it everywhere.

Last solution I currently use is messing up the IE rendering engine and force it to render the absolutely positioned div as an ActiveX element too, ensuring it can live over a select element. This is achieved by placing an invisible iframe inside the div and styling it with:

#MyDiv iframe
{
    position: absolute;
    z-index: -1;
    filter: mask();
    border: 0;
    margin: 0;
    padding: 0;
    top: 0;
    left: 0;
    width: 9999px;
    height: 9999px;
    overflow: hidden;
}

Anyone has a even better solution than this one ?

EDIT: The purpose of this question is as much informative as it is a real question. I find the iframe trick to be a good solution but I am still looking for improvement like removing this ugly useless iframe tag that degrade accessibility.