This property indicates the width the Collapse / Restore button when the splitter is docked to the top of bottom. It indicates the Height of the button when the splitter is docked left or right.
A value of 0 indicates that the default extent will be used.
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