* {
    margin: 0;
    padding: 0;
}

body {
    max-width: 720px;
    text-align: center;
    margin: 0 auto;
}

.box {
    width: 100%;
    position: relative;
    max-width: 720px;
}

.logo {
    position: absolute;
    width: 42%;
    top: 15px;
    left: 50%;
    transform: translateX(-50%);
    z-index: 3;
}

.w100 {
    width: 100%;
}

img {
    display: block;
}

.bt01 {
    display: block;
}

.top {
    position: sticky;
    top: 0;
    z-index: 10;
}

.down {
    position: fixed;
    bottom: 0;
    left: 50%;
    transform: translateX(-50%);
    width: 100%;
    z-index: 1;
    max-width: 720px;
}

.kefu {
    position: fixed;
    /* 保持固定位置，随滚动条移动 */
    right: 0;
    width: 23%;
    top: 45%;
    max-width: 200px;
    z-index: 2;
    animation: moveUpDown 0.6s infinite alternate;
}

@keyframes moveUpDown {
    0% {
        transform: translateY(0);
    }

    100% {
        transform: translateY(5px);
    }
}

.bt02 {
    display: block;
}