css 蒙层利用伪元素做蒙层:

蒙层

 

利用z-index:

.mui-backdrop-other {
position: fixed;
top: 44px;
right: 0;
bottom: 0;
left: 0;
z-index: 2;
background-color: rgba(0, 0, 0, .3);
}

 

利用伪元素做蒙层:

.element {
position: relative;
}
.element:after {
content: "哈哈哈，我是遮罩";
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
box-sizing: border-box;
padding: 100px;
background-color: rgba(0, 0, 0, .6);
color: #fff;
text-align: center;
}