Make Scrollbar translucent.

src/ui/Scrollbar.cpp

@@ -32,6 +32,7 @@ void Scrollbar::draw(const DrawArgs& args) {
 
 	float handleOffset = sw->getHandleOffset()[vertical];
 	float handleSize = sw->getHandleSize()[vertical];
+	nvgAlpha(args.vg, 0.5);
 	bndScrollBar(args.vg, 0.0, 0.0, box.size.x, box.size.y, state, handleOffset, handleSize);
 }