#d1 {
position: absolute;
width: 300px;
height: 300px;
visibility: hidden;
color: #fff;
background: #555;
}
#d2 {
position: absolute;
width: 300px;
height: 300px;
visibility: hidden;
color: #fff;
background: #777;
}
#d3 {
position: absolute;
width: 150px;
height: 150px;
visibility: hidden;
color: #fff;
background: #999;
}
d1
d2
d2包含d3
d3
d3是d2的子层