@keyframes arrow-opacity-in {
    /* You could think of as "step 1" */
    0% {
        opacity: 1;
        padding-left: 0;
    }
    /* You could think of as "step 2" */
    100% {
        padding-left: 10px;
        opacity: 1;
    }
}

@keyframes arrow-opacity-out {
    /* You could think of as "step 1" */
    0% {
        padding-left: 10px;
        opacity: 1;
    }

    /* You could think of as "step 2" */
    100% {
        opacity: 1;
        padding-left: 0;
    }
}