MouseOverStyles
All controls have two sets of styles: Styles and MouseOverStyles.
Styles are applied to the control and any child controls.
MouseOver Styles are applied to the control on MouseOver, i.e. when the mouse enters the bounds of the control, and removed on MouseLeave. This allows for simple declarative code rather than having to code lots of MouseEnter events.
Composite controls such as Panel and Group box have a third set of styles, PrivateStyles. Private Styles allow composites to continue to use the styles supplied by their parent, and to have their own styles that aren’t passed on to child controls. For example they can make a group box caption red without making the contents red.