I'd like to add a new ID like:
#sub-header {
z-index: 100;
border-radius: 5px;
}
which I've added to custom.css to define the image in module postion top-1a
but it doesn't have any effect and does not show up in "inspect elements"
I've created a Custom HTML module to hold the image
<div id="sub-header"><img src="images/headers/subHeader980x71_powering.jpg" alt="" /></div>
I also want it to appear in front of everything around it so have used z-index:100; but doesn't work.

The image appears below and behind the header image above, see http://j31.thesciencecouncil.com/

What am I missing?

thanks,

keith