Gets the alpha transparency values used for the background fill of components.
Set this to an Array of either two or four numbers. Elements 0 and 1 specify the start and end values for an alpha gradient. If elements 2 and 3 exist, they are used instead of elements 0 and 1 when the component is in a mouse-over state. The global default value is [ 0.60, 0.40, 0.75, 0.65 ]. Some components, such as the ApplicationControlBar container, have a different default value. For the ApplicationControlBar container, the default value is [ 0.0, 0.0 ].
Deprecated Since 3.0: Use headerStyleName