<div>
    <p>毛玻璃效果</p>
</div>

$img: 'https://images.unsplash.com/photo-1440688807730-73e4e2169fb8?dpr=1&auto=format&fit=crop&w=1500&h=1001&q=80&cs=tinysrgb&crop=';

html,
body {
    width: 100%;
    height: 100%;
    background-image: url($img);
    background-repeat: no-repeat;
    background-attachment: fixed;
    background-size: cover;
    background-position: top;
    overflow: hidden;
}

div {
    position: relative;
    width: 30vw;
    height: 40vh;
    background: inherit;
    margin: 50px auto;
    padding: 5vmin;
    border-radius: 5px;
    border: 2px solid rgba(255, 255, 255, .5);
    // transform: translate(-50%, -50%);
    // left: 50%;
    // top: 50%;

    p {
        position: relative;
        color: #000;
        z-index: 10;
        font-size: 24px;
        line-height: 1.5;

    }

    &::after {
        position: absolute;
        content: "";
        background: inherit; 
        top: 0;
        left: 0;
        right: 0;
        bottom: 0;
        filter: blur(10px);
        z-index: 0;
    }
}