message: Constrain becomes a mixin incase you want to... mix it in
diff: height 100%
  overflow hidden
  -.Constrain
  +constrain()
  for i in (1..8)
  @media (min-width: (block_width_mar * i) + unit)
  center(block_width_mar * i)
  @media (max-width: (block_width_mar * 3) + unit)
  center(90%)
  +.Constrain
  + constrain()
  +
  &--narrow
  max-width (block_width_mar * 2)
  