The button class is notified by the .net framework via the IButtonControl interface when it becomes the default button. This allows the button to modify its appearance to indicate its changed state. When the button is the default button, it will show an extra outline around the border of the control. This appearance change can be prevented using the ShowOutline property.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Server 2012, Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2