1.毛玻璃效果：背景圖 + 偽類 + flite:blur(3px)

image

.demo1{
    width: 500px;
    height: 300px;
    line-height: 50px;
    text-align: center;
}
.demo1:before{
    background: url(http://csssecrets.io/images/tiger.jpg) no-repeat;
    background-size: cover;
    width: 500px;
    height: 300px;
    content: "";
    position: absolute;
    top: 0;
    left: 0;
    z-index: -1;/*-1 可以當(dāng)背景*/
    -webkit-filter: blur(3px);
    filter: blur(3px);
}

<div class="demo1">背景圖半透明，文字不透明<br />方法：背景圖+ filter：blur</div>

2.半透明效果：背景圖 + 定位 + background:rgba(255,255,255,0.3)

image

.demo2-bg{
    background: url(http://csssecrets.io/images/tiger.jpg) no-repeat;
    background-size: cover;
    width: 500px;
    height: 300px;
    position: relative;
}
.demo2{
    position: absolute;
    left: 0;
    right: 0;
    top: 0;
    bottom: 0;
    width: 500px;
    height: 300px;
    line-height: 50px;
    text-align: center;
    background:rgba(255,255,255,0.3);
}


<div class="demo2-bg">
    <div class="demo2">背景圖半透明，文字不透明<br />方法：定位+ background:rgba(255,255,255,0.3)</div>
</div>

來源