html,
body {
    overflow-x: hidden;
    overflow-y: hidden;
}

html {
    scroll-behavior: smooth;
}

.topImg {
    position: absolute;
    width: 100vw;
    height: 100vh;
    top: 0;
    left: 0;
    z-index: 999;
    object-fit: contain;
    object-position: center;
    overflow: hidden;
}

.bottomImg {
    position: absolute;
    top: 0;
    left: 0;
    width: 100vw;
    height: 100vh;
    z-index: 998;
    object-fit: contain;
    object-position: center;
    overflow: hidden;
}

.bgImg {
    position: absolute;
    width: 100vw;
    height: auto;
    top: 0;
    left: 0;
    object-fit: contain;
    object-position: center;
    opacity: 0; /*刚开始隐藏*/
}


.downImg {
    position: fixed;
    width: 40px;
    height: 40px;
    bottom: 20px;
    left: 50%;
    z-index: 99;
    transform: translate(-50%, 0);
    object-fit: contain;
    object-position: center;
    opacity: 0; /*刚开始隐藏*/
}


/*下面是动画*/

.is_animate_top {
    animation: my_animation 1.5s ease-in-out;
    animation-iteration-count: 1;
    animation-fill-mode: forwards;
}


@keyframes my_animation {
    0% {
    }

    100% {
        transform: translateY(-100%);
    }
}

.is_animate_bottom {
    animation: my_animation2 2s ease-in-out;
    animation-iteration-count: 1;
    animation-fill-mode: forwards;
}


@keyframes my_animation2 {
    0% {
    }

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


.is_animate_bg {
    animation: my_animation3 0.6s ease-in;
    animation-iteration-count: 1;
    animation-fill-mode: forwards;
}

@keyframes my_animation3 {
    0% {
        opacity: 0;
    }

    100% {
        opacity: 1;
    }
}