It depends on the type of project. The HIghlight box can be used while the outer area is dimmed, which is the easiest solution but only possible with a rectangular shape. Because you are covering up, stacking objects this standard object type is not supported for responsive projects, Fluid Boxes workflow. Same restriction for the solution by Rod because that also needs object stacking. For that type of projects to avoid having to limit the fluid boxes layout control by switching to Static fluid boxes, I can only recommend multistate objects.