遮罩层
.box{
position:absolute;
top:0;
bottom:0;
left:0;
right:0;
background:#000;
opacity:0.7;
}
<div class="box"></div>
.box{
position:absolute;
top:0;
bottom:0;
left:0;
right:0;
background:#000;
opacity:0.7;
}
<div class="box"></div>