.backToTop {
    background-image: url("../src/taichi.png");
    background-size: cover;
    position: fixed;
    bottom: 180px;
    right: 100px;
    display: none; 
    border: none;
    width: 50px;
    height: 50px;
    border-radius: 50%;
    cursor: pointer;
    z-index: 99;
    animation: xuanzhuan infinite 10s;
}
@keyframes xuanzhuan {
    0% {
        transform: rotate(0deg);
    }
    100% {
        transform: rotate(360deg);
    }
}

.backToTop:hover {
    background-image: url("../src/置顶.png");
    animation: none;
    z-index: 99;
}