a {
    -webkit-animation-direction: alternate;
         -o-animation-direction: alternate;
            animation-direction: alternate;
    animation-direction: reverse;
    animation-direction: REVERSE;
    animation-direction: alternate-reverse;
    -webkit-animation: rotation-reverse;
         -o-animation: rotation-reverse;
            animation: rotation-reverse;
    animation: rotation-reverse reverse;
}
