The description box that pops up when you click on a map object (area, image, or just about anything else) that has a "description" property is basically a <div> element that can be customized like any HTML element.
To do that use the following CSS classes:
|CSS Class||Applies to|
|ammapDescriptionWindow||The whole description box window (outer container). You might want to set background / borders in this class.|
|ammapDescriptionWindowCloseButton||Close button. You can use it to reposition, change color or even override the image itself here.|
|ammapDescriptionTitle||The title that appears at the top of the description box. By default it contains the title of the clicked object.|
|ammapDescriptionText||Body of the description box. That's where everything from "description" property goes into.|
As for the contents of the description box, it can contain any valid HTML including CSS-styled elements.