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                nav Hover Me... ... then me ... ... and me, because we even work with a line break. We flash when you click us.


                ease-out-swift = cubic-bezier(.55,0,.1,1)
//basic interactive element styles
  font-size 30px
  color black
  font-family Helvetica
  display inline-block
  height 100%
  padding 30px
  width auto
  position relative
  cursor pointer
  transition 0.3s ease-out-swift
.interactive:active //cool click effect
  transition none
  color white
  background black

.in-array:before // create a pseudo element with zero width 
  left 100% // THE TRICK: we assume that, by default, the cursor is on one of the following in-arrays. The line is aligned to the right of it's container :P
  transition 0.3s ease-out-swift
  content ''
  position absolute
  height 100%
  border-bottom 2px solid black
  width 0
  top 0

//but when we hover a in-array, the pseudo elements of this AND the following in-arrays get aligned to the left side of the in-array
    border-bottom-color black
    width 100%
    top 0
    transition-delay 0.1s // bridgin the distance between elements
    left 0 //THE TRICK
  & ~ .in-array:before
    left 0 //THE TRICK