/* 使用flex布局，让内容垂直和水平居中 */
    section {
        /* 相对定位 */
        position: relative;
        overflow: hidden;
        display: flex;
        justify-content: center;
        align-items: center;
        min-height: 100vh;
        /* linear-gradient() 函数用于创建一个表示两种或多种颜色线性渐变的图片 */
        background: linear-gradient(to bottom, #f1f4f9, #dff1ff);
    }

    /* 背景颜色 */
    section .color {
        /* 绝对定位 */
        position: absolute;
        /* 使用filter(滤镜) 属性，给图像设置高斯模糊*/
        filter: blur(200px);
    }

    /* :nth-child(n) 选择器匹配父元素中的第 n 个子元素 */
    section .color:nth-child(1) {
        top: -350px;
        width: 600px;
        height: 600px;
        background: #ff359b;
    }

    section .color:nth-child(2) {
        bottom: -150px;
        left: 100px;
        width: 500px;
        height: 500px;
        background: #fffd87;
    }

    section .color:nth-child(3) {
        bottom: 50px;
        right: 100px;
        width: 500px;
        height: 500px;
        background: #00d2ff;
    }

    .box {
        position: relative;
    }

    /* 背景圆样式 */
    .box .circle {
        position: absolute;
        background: rgba(255, 255, 255, 0.1);
        /* backdrop-filter属性为一个元素后面区域添加模糊效果 */
        backdrop-filter: blur(5px);
        box-shadow: 0 25px 45px rgba(0, 0, 0, 0.1);
        border: 1px solid rgba(255, 255, 255, 0.5);
        border-right: 1px solid rgba(255, 255, 255, 0.2);
        border-bottom: 1px solid rgba(255, 255, 255, 0.2);
        border-radius: 50%;
        /* 使用filter(滤镜) 属性，改变颜色。
    hue-rotate(deg)  给图像应用色相旋转 
    calc() 函数用于动态计算长度值 
    var() 函数调用自定义的CSS属性值x*/
        filter: hue-rotate(calc(var(--x) * 70deg));
        /* 调用动画animate，需要10s完成动画，
    linear表示动画从头到尾的速度是相同的，
    infinite指定动画应该循环播放无限次*/
        animation: animate 10s linear infinite;
        /* 动态计算动画延迟几秒播放 */
        animation-delay: calc(var(--x) * -1s);
    }

    /* 背景圆动画 */
    @keyframes animate {

        0%,
        100%,
        {
        transform: translateY(-50px);
    }

    50% {
        transform: translateY(50px);
    }
    }

    .box .circle:nth-child(1) {
        top: -50px;
        right: -60px;
        width: 100px;
        height: 100px;
    }

    .box .circle:nth-child(2) {
        top: 150px;
        left: -100px;
        width: 120px;
        height: 120px;
        z-index: 2;
    }

    .box .circle:nth-child(3) {
        bottom: 50px;
        right: -60px;
        width: 80px;
        height: 80px;
        z-index: 2;
    }

    .box .circle:nth-child(4) {
        bottom: -80px;
        left: 100px;
        width: 60px;
        height: 60px;
    }

    .box .circle:nth-child(5) {
        top: -80px;
        left: 140px;
        width: 60px;
        height: 60px;
    }

    /* 登录框样式 */
    #section .container {
        position: relative;
        width: 450px;
        min-height: 400px;
        background: rgba(255, 255, 255, 0.1);
        display: flex;
        justify-content: center;
        align-items: center;
        backdrop-filter: blur(5px);
        box-shadow: 0 25px 45px rgba(0, 0, 0, 0.1);
        border: 1px solid rgba(255, 255, 255, 0.5);
        border-right: 1px solid rgba(255, 255, 255, 0.2);
        border-bottom: 1px solid rgba(255, 255, 255, 0.2);
    }

    .form {
        position: relative;
        width: 100%;
        height: 100%;
        padding: 50px;
    }

    /* 登录标题样式 */
    .form h2 {
        position: relative;
        color: #000;
        font-size: 24px;
        font-weight: 600;
        letter-spacing: 5px;
        margin-bottom: 30px;
        cursor: pointer;
    }

    /* 登录标题的下划线样式 */
    .form h2::before {
        content: "";
        position: absolute;
        left: 0;
        bottom: -10px;
        width: 0px;
        height: 3px;
        background: #000;
        transition: 0.5s;
    }

    .form h2:hover:before {
        width: 53px;
    }

    .form .inputBox {
        width: 100%;
        margin-top: 20px;
    }

    input::placeholder {
        color: #999 !important
    }

    /* 输入框样式 */
    .form .inputBox input {
        width: 100%;
        padding: 10px 20px;
        background: rgba(255, 255, 255, 0.2);
        outline: none;
        border: none;
        border-radius: 30px;
        border: 1px solid rgba(255, 255, 255, 0.5);
        border-right: 1px solid rgba(255, 255, 255, 0.2);
        border-bottom: 1px solid rgba(255, 255, 255, 0.2);
        font-size: 16px;
        letter-spacing: 1px;
        color: #333;
        box-shadow: 0 5px 15px rgba(0, 0, 0, 0.05);
    }

    .form .inputBox input::placeholder {
        color: #fff;
    }

    /* 登录按钮样式 */
    .form .inputBox input[type="submit"] {
        background: #fff;
        color: #666;
        max-width: 100px;
        margin-bottom: 20px;
        font-weight: 600;
        cursor: pointer;
    }

    .forget {
        margin-top: 6px;
        color: #fff;
        letter-spacing: 1px;
    }

    .forget a {
        color: #fff;
        font-weight: 600;
        text-decoration: none;
    }