@keyframes spin {
    from { transform: rotate(0deg); }
    to { transform: rotate(360deg); }
}

@keyframes flow {
    0% {
        background-position: 0% 50%;
    }
    50% {
        background-position: 100% 50%;
    }
    100% {
        background-position: 0% 50%;
    }
}

@keyframes spin-reverse {
    from { transform: rotate(0deg); }
    to { transform: rotate(-360deg); } /* 注意这里是负号，代表反着转 */
}

@keyframes bg-flow {
    0% { background-position: 0% 50%; }
    50% { background-position: 100% 50%; }
    100% { background-position: 0% 50%; }
}