#main {position:relative;}
.black, .red, .blue, .green {
position:absolute;
border:3px dotted #000;
background:#FFF;
z-index:10;
}
.content {position:relative;margin:10px;}
.black {top:300px;left:103px;z-index:9;}
.black .content {height:180px;width:280px;background:#000;}
.blue{ top:50px;left:200px;border-bottom:none;}
.blue .content {height:30px;width:30px;background:#009;}
.red{top:0px;left:0px;}
.red .content {height:280px;width:80px;background:#F00;}
.green{top:100px;left:103px;border-left:none;border-bottom:none;}
.green .content{height:180px;width:180px;background:#070;}