Try this approach:
procedure TMainForm.UniButton1Click(Sender: TObject);
begin
//UniContainerPanel1.ScrollBy(-100,0); //not working
UniContainerPanel1.JSInterface.JSCall('getScrollable().scrollBy', [-100, 0]);
end;
procedure TMainForm.UniButton2Click(Sender: TObject);
begin
//UniContainerPanel1.ScrollBy(100,0); //not working
UniContainerPanel1.JSInterface.JSCall('getScrollable().scrollBy', [100, 0]);
end;