Using rect.width & rect.height instead of sizeDelta.
Like that you can have the top container use stretch anchors
--HG--
branch : Ziboo/change-how-children-are-resize-using-rec-1443606808122
It seems to have a bug on the last row, elements go out of bounds on the right, I think I fixed it by removing "SpacingX" of the "workingWidth" on the last row.
Line 168
--HG--
branch : Ziboo/flowlayoutgroupcs-edited-online-with-bit-1443606102163