Determines whether the animation should play in reverse on alternate iterations.
-webkit-animation-direction: <direction> [, …];
The direction to play.
normal (by default) Play each iteration of the animation in the forward direction. alternate
Play 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.