title: Flip vertically a background-image every time it repeat-y
body: <p>I'm searching for a trick that repeat my background image vertically, but every time the image is repeated I want to flip it vertically.</p>
  
  <p>I tried all the things in my mind with repeat-y but I don't found a solution, even searching for it in google.</p>
  
  <p>Example:</p>
  
  <p><img src="https://i.stack.imgur.com/I4hlZ.png" alt="Background"> Straight background-image</p>
  
  <p><img src="https://i.stack.imgur.com/qKqir.png" alt="Background flipped vertically"> Flipped background-image when it repeat-y</p>
  
  <p><img src="https://i.stack.imgur.com/I4hlZ.png" alt="Background flipped vertically again"> And then flipped again to straight</p>
  
  <p>There is a method to obtain that position?</p>
  
  <p>I'll accept the solution in JScript (and library of it) only if there isn't a solution with pure css. </p>
  
  <p>Thank you all!</p>