<div class=‘big‘>        <div class=‘small‘>box1</div>  </div>style样式：.big{  height:200px;  width:200px;  border:black solid 1px;  position:absolute;  left:150px;  }.small{  height:100px;  width:100px;  background-color:green;  position:relative;  left:100px;  top:100px;  margin-top:-50px;  margin-left:-50px;  border:black solid 1px;}

div class=‘big2‘>        <div class=‘small2‘>box3</div>  </div>.big2{  height:200px;  width:200px;  border:black solid 1px;  text-align:center;}.small2{  height:100px;  width:100px;  background-color:green;  margin:50px auto; //外面的div高度的一半  border:black solid 1px;}