层级 背影

.box1{

width:200px;

height:200px;

background-color:#0bcd96;

position:relative;z-index:3; 

}

.box2{

width:200px;

height:200px;

background-color:#1e389a;

position: absolute;left:100px;top:100px; 

}

.box3{

width:200px;

height:200px;

background-color:#6a1752;

position: relative;z-index:2;

 }

背影

.box1{

width:400px;

height:300px;

margin:0auto;

background-color:#000;

background-image:url(../css/[email protected]);

background-repeat:no-repeat;

 }