If what you want is to put the map inside a div and then have other divs shown over it you have to use these CSS properties:
position: relative;
position: absolute;
and place the div that's going over, inside the first one. For example, I use a construction like this:
<div style="position: relative;">
<div style="position: absolute">here goes the map</div>
<div style="position: absolute; z-index: 10">
here goes the error message that's going to show up over the map
</div>
</div>