Also, if you wish to place elements relative to a particular corner or edge of the window, you should parent them to one of the following nodes instead of base.aspect2d:
base.a2dTopLeft
base.a2dTopRight
base.a2dBottomLeft
base.a2dBottomRight
base.a2dTopCenter
base.a2dBottomCenter
base.a2dLeftCenter
base.a2dRightCenter