The CSS-webkit-animation-directionApple extension property determines whether the animation should play in reverse on alternate iterations.
The direction to play. The default is normal.
Plays each iteration of the animation in the forward direction.
Plays even-numbered iterations of the animation in the forward direction and odd-numbered iterations in the reverse direction. When an animation is played in reverse, the timing functions are also reversed. For example, when played in reverse, an ease-in animation appears as an ease-out animation.