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@charset "utf-8";
/* CSS Document */
*
{
    margin:0px;
}

.a
{
    width:100px;
    height:50px;
    top:20px;
    left:20px;    
    background-color:red;
    position:absolute;
    overflow:hidden;
    }
.a:hover
{
    overflow:visible;}

.aa
{
    width:100px;
    height:150px;
    top:50px;
    left:20px;
    background-color:black;
    position:absolute;
    }
    
.b
{
    width:100px;
    height:50px;
    top:50px;
    left:0px;
    background-color:blue;
    position:absolute;
    overflow:hidden;
    }
.b:hover
{
    overflow:visible;}

.bb
{
    width:100px;
    height:150px;
    top:0px;
    left:100px;
    background-color:blue;
    position:absolute;
    }


.c
{
    width:100px;
    height:50px;
    top:100px;
    left:0px;
    background-color:yellow;
    position:absolute;
    overflow:hidden;
    }
.c:hover
{
    overflow:visible;}
    
.cc
{
    width:100px;
    height:150px;
    top:0px;
    left:100px;
    background-color:yellow;
    position:absolute;
    }
    
    
.d
{
    width:100px;
    height:50px;
    top:150px;
    left:0px;
    background-color:green;
    position:absolute;
    overflow:hidden;
    }
.d:hover
{
    overflow:visible;}

.dd
{
    width:100px;
    height:150px;
    top:0px;
    left:100px;
    background-color:green;
    position:absolute;
    }

<body>

<div class="a">
    <div id="aa">
        <div class="b"><div class="bb"></div></div>

        <div class="c"><div class="cc"></div></div>

        <div class="d"><div class="dd"></div></div>

    </div>
</div>

</body>
</html>

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原文地址：https://www.cnblogs.com/xiao55/p/5531627.html