<style type="text/css">
div.grid {
position:relative;
width:200px; height:200px;
margin:0; padding:0;
background:#fff url(/content/img/css/grid.gif) repeat top left;
}
div.grid div.pos_top {
position:absolute;
top:20px; /* 親ボックスの上辺から下方向へ20pxの位置 */
width:100px; height:100px;
}
</style>
<div class="grid">
<div class="pos_top"><img src="/content/img/100x100.gif" alt="100x100" width="100" height="100" /></div>
</div>