<div?id="container">
????<div?id="header">
????????<div?id="header_middle"></div>
????</div>
????<div?id="main"></div>
????<div?id="content"></div>
????<div?id="footer"></div>
</div>

*{
????margin:?0;
????padding:?0;
}
#container{
????width:?100%;
}
#header{
????height:?60px;
????background:?blue;
}
#header_middle{
????height:?100%;
????width:?1200px;
????background:?gray;
????margin:?0?80px;
}
#main{
????height:?300px;
????background:?red;
}
#content{
????height:?300px;
????background:?purple;
}
#footer{
????height:?300px;
????background:?orange;
}

就這么個結構吧，有黃色啊，你沒看到黃色是不是因為content尺寸太大，你沒有往下滑動繼續看？