'padding-bottom' + 'border-bottom-width' + 'margin-bottom' + 'bottom' = height of containing block

So:

  (solve) : top: auto
  +
      0px : margin-top
  +
      0px : border-top-width
  +
      0px : padding-top
  +
     80px : height
  +
      0px : padding-bottom
  +
      0px : border-bottom-width
  +
      0px : margin-bottom
  +
    160px : bottom: auto: set to static position
    =====================
    320px : height of containing block

And so computed top value must be 80px .
*/

  ]]></style>