/* 添加关键帧动画 */
@keyframes animate {
    0%{
        transform: translateY(0) rotate(0deg);
        opacity: 1;
        border-radius: 0;
    }
    100%{
        transform: translateY(-1000px) rotate(720deg);
        opacity: 0;
        border-radius: 50%;
    }
}

/* 动态背景样式 */
.background {
    position: fixed;
    width: 100vw;
    height: 100vh;
    top: 0;
    left: 0;
    margin: 0;
    padding: 0;
    overflow: hidden;
    z-index: -1; /* 确保在内容下方 */
}
.background li {
    position: absolute;
    display: block;
    list-style: none;
    width: 20px;
    height: 20px;
    background: rgba(255, 255, 255, 0.2);
    animation: animate 19s linear infinite;
}

/* 各粒子样式 */
.background li:nth-child(1) {
    left: 33%;
    width: 51px;
    height: 51px;
    bottom: -51px;
    animation-delay: 1s;
}
.background li:nth-child(2) {
    left: 63%;
    width: 99px;
    height: 99px;
    bottom: -99px;
    animation-delay: 1s;
}
.background li:nth-child(3) {
    left: 64%;
    width: 56px;
    height: 56px;
    bottom: -56px;
    animation-delay: 6s;
}
.background li:nth-child(4) {
    left: 30%;
    width: 66px;
    height: 66px;
    bottom: -66px;
    animation-delay: 4s;
}
.background li:nth-child(5) {
    left: 4%;
    width: 83px;
    height: 83px;
    bottom: -83px;
    animation-delay: 8s;
}
.background li:nth-child(6) {
    left: 55%;
    width: 43px;
    height: 43px;
    bottom: -43px;
    animation-delay: 7s;
}
.background li:nth-child(7) {
    left: 85%;
    width: 98px;
    height: 98px;
    bottom: -98px;
    animation-delay: 4s;
}
.background li:nth-child(8) {
    left: 9%;
    width: 85px;
    height: 85px;
    bottom: -85px;
    animation-delay: 5s;
}
.background li:nth-child(9) {
    left: 10%;
    width: 47px;
    height: 47px;
    bottom: -47px;
    animation-delay: 28s;
}
.background li:nth-child(10) {
    left: 67%;
    width: 100px;
    height: 100px;
    bottom: -100px;
    animation-delay: 11s;
}
.background li:nth-child(11) {
    left: 40%;
    width: 86px;
    height: 86px;
    bottom: -86px;
    animation-delay: 36s;
}
.background li:nth-child(12) {
    left: 37%;
    width: 72px;
    height: 72px;
    bottom: -72px;
    animation-delay: 34s;
}
.background li:nth-child(13) {
    left: 17%;
    width: 89px;
    height: 89px;
    bottom: -89px;
    animation-delay: 32s;
}