<style type="text/css">
#d1 {
        background-color: red;
}
#d2 {
        height: 100px;
        background-color: green;
}
#d3 {
        margin: 10px;
        background-color: blue;
}
</style>

<div id="d1">
I'm d1.
</div>
<div id="d2">
        <div id="d3">
        I'm d3.
        </div>
        I'm d2.
</div>

效果见附件，为什么在firefox中, d2的top会出现一条空白？
--
修改:Keyn FROM 117.79.72.*
FROM 117.79.72.*