怎樣做到#wrap頂部和底部與瀏覽器無間距？

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<html xmlns="http://www.w3.org/1999/xhtml">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>無標題文檔</title>
<style type="text/css">
*{margin:0; padding:0;}
#wrap{width:970px; margin:0 auto;}
#mainbody{position: relative; margin-top:15px; width: 100%; overflow: hidden;}
#left{float: left; width:110px; margin-left: 13px;}
#mid{float: left; width:650px;border:1px solid #999;}
#right{position: absolute; left: 790px; top: 0px; border:1px solid #999;}
</style>
</head>
<body>
<div id="wrap">
? ? <div id="header"><img src="http://img1.sycdn.imooc.com//5369cd6e0001a15b09700088.jpg" width="970" height="88" /></div>
? ? <div id="mainbody">
? ? ? ? ?<div id="left"><img src="http://img1.sycdn.imooc.com//5369cd0e00011e3901090487.jpg" width="109" height="487" /></div>
? ? ? ? ?<div id="mid"><img src="http://img1.sycdn.imooc.com//5369cd3c00013e9e06490439.jpg" width="649" height="439" /></div>
? ? ? ? ?<div id="right"><p>歡迎使用金山軟件出品的愛詞霸，在線查詢你英語詞匯、句子釋義</p><img src="http://img1.sycdn.imooc.com//5369cd540001d8e101770329.jpg" width="177" height="329" /></div>
?</div>
</div>
</body>
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