How to place animation in a child theme in wordpress

Hi, how would I put the following animation code in a child theme.:

.flip-horizontal-bottom {
-webkit-animation: flip-horizontal-bottom 0.4s cubic-bezier(0.455, 0.030, 0.515, 0.955) both;
animation: flip-horizontal-bottom 0.4s cubic-bezier(0.455, 0.030, 0.515, 0.955) both;
}

* —————————————-
* animation flip-horizontal-bottom
* —————————————-
*/
@-webkit-keyframes flip-horizontal-bottom {
0% {
-webkit-transform: rotateX(0);
transform: rotateX(0);
}
100% {
-webkit-transform: rotateX(-180deg);
transform: rotateX(-180deg);
}
}
@keyframes flip-horizontal-bottom {
0% {
-webkit-transform: rotateX(0);
transform: rotateX(0);
}
100% {
-webkit-transform: rotateX(-180deg);
transform: rotateX(-180deg);
}
}