/* 背景方块动画 */
@keyframes square { /* 方块自定义定义动画 */
    0%{
        transform: translateY(0);
    }
    100%{
        transform: translateY(calc(-100vh - 160px)) rotate(900deg);
    }
}
.main-background li{
    /* 执行动画：动画名 时长 线性 无限次播放 */
    animation: square 28s linear infinite;
}
    /* 为每一个方块设置不同的位置、大小、动画延迟时间、动画时长、背景色 */
    .main-background li:nth-child(1){
        left: 5%;
        animation-delay: 4s;
    }
    .main-background li:nth-child(2){
        left: 20%;
        width: 80px;
        height: 80px;
        border-radius: 10px;
        /* 动画延迟时间 */
        animation-delay: 2s;
        /* 动画时长 */
        animation-duration: 17s;
    }
    .main-background li:nth-child(3){
        left: 25%;
        animation-delay: 4s;
        background-color: rgba(255,255,255,0.35);
    }
    .main-background li:nth-child(4){
        left: 40%;
        width: 60px;
        height: 60px;
        border-radius: 7.5px;
        background-color: rgba(255,255,255,0.25);
        animation-duration: 22s;
    }
    .main-background li:nth-child(5){
        left: 60%;
        animation-delay: 5s;
        background-color: rgba(9,132,227,0.05);
    }
    .main-background li:nth-child(6){
        left: 80%;
        width: 120px;
        height: 120px;
        border-radius: 15px;
        background-color: rgba(255,255,255,0.2);
        animation-delay: 3s;
    }
    .main-background li:nth-child(7){
        left: 32%;
        width: 150px;
        height: 150px;
        border-radius: 20px;
        animation-delay: 9s;
        background-color: rgba(255,255,255,0.1);
    }
    .main-background li:nth-child(8){
        left: 55%;
        width: 20px;
        height: 20px;
        border-radius: 2.5px;
        animation-delay: 15s;
        animation-duration: 40s;
        background-color: rgba(9,132,227,0.2);
    }
    .main-background li:nth-child(9){
        left: 25%;
        width: 10px;
        height: 10px;
        border-radius: 1.5px;
        background-color: rgba(255,255,255,0.3);
        animation-delay: 2s;
        animation-duration: 40s;
    }
    .main-background li:nth-child(10){
        left: 80%;
        width: 160px;
        height: 160px;
        border-radius: 20px;
        animation-delay: 11s;
        animation-duration: 35s;
        background-color: rgba(255,255,255,0.1);
    }
    .main-background li:nth-child(11){
        left: 70%;
        width: 120px;
        height: 120px;
        border-radius: 20px;
        animation-delay: 16s;
        animation-duration: 30s;
        background-color: rgba(255,255,255,0.15);
    }
    .main-background li:nth-child(12){
        left: 60%;
        width: 40px;
        height: 40px;
        border-radius: 10px;
        animation-delay: 9s;
        animation-duration: 40s;
        background-color: rgba(9,132,227,0.1);
    }
    .main-background li:nth-child(13){
        left: 25%;
        width: 80px;
        height: 80px;
        border-radius: 20px;
        animation-delay: 20s;
        background-color: rgba(9,132,227,0.25);
    }
    .main-background li:nth-child(14){
        left: 45%;
        width: 70px;
        height: 70px;
        border-radius: 20px;
        animation-delay: 13s;
        animation-duration: 20s;
        background-color: rgba(9,132,227,0.3);
    }
    .main-background li:nth-child(15){
        left: 35%;
        width: 140px;
        height: 140px;
        border-radius: 25px;
        animation-delay: 6s;
        background-color: rgba(9,132,227,0.1);
    }