I was looking for some member function in ScrollBar to retieve the scrollbar size, or expose the const Style *style
which can in turn access the barsize value, but to no avail. Until I find this function

inline int ScrollBarSize()                  { return ScrollBar::StyleDefault().barsize; }//!!

A search in the Upp src indicates many libraries make use of this function, including in HeaderCtrl

void HeaderCtrl::FrameLayout(Rect& r)
{
	LayoutFrameTop(r, this, invisible ? 0 : GetHeight());
	LayoutFrameBottom(r, &sb, sb.IsShown() ? ScrollBarSize() : 0);
}

void HeaderCtrl::FrameAddSize(Size& sz)
{
	if(!invisible)
		sz.cy += GetHeight();
	if(sb.IsVisible())
		sz.cy += ScrollBarSize();
}

Does this imply that a customized ScrollBar Style shall not disagree on barsize with the default ScrollBar Style? Is this restriction necessary? or shall we expose int ScrollBar::ScrollBarSize()const(elevate it to a public member function from a private one as it is now)?