Choose Format - Arrange - Send Backward (LibreOfficeDev Writer, LibreOfficeDev Calc).
Choose Shape - Arrange - Send Backward (LibreOfficeDev Draw).
(Command)(Ctrl) + (-) 記号 (LibreOfficeDev Impress, LibreOfficeDev Draw)
Open context menu - choose Arrange - Send Backward (LibreOfficeDev Impress).