gistfile1.sass

.followheader
  $h: 50px
  @keyframes enter
    from
      top: -$h
    to
      top: 0px

  @keyframes leave
    from
      top: 0px
    to
      top: -$h

  position: absolute
  top: 0
  left: 0
  width: 100%
  z-index: 999
  height: $h
  &.is-open
    position: fixed
    animation: enter 0.3s ease-out
    top: 0
  &.is-close
    position: fixed
    animation: leave 0.3s ease-out
    top: -$h