Returns the current scroll bar style
It can be one of the following values defined by CBCGPScrollBar::BCGPSB_STYLE enumerator:
- BCGP_SBSTYLE_DEFAULT: Windows default style (not owner draw)
- BCGP_SBSTYLE_VISUAL_MANAGER: Defined by currently activated Visual Manager
- BCGP_SBSTYLE_VISUAL_MANAGER_FRAME: Scroll bar is hosted by a frame window and drawn differently than in control
- BCGP_SBSTYLE_OWNER_DRAW: A developer should handle BCGM_ON_DRAW_SCROLLBAR message
