CSS浮動
結論，非浮動元素可以為後面的浮動元素定位， 但是 浮動元素無法再為其後的非浮動元素定位。
No-float A + Float B + No-float C
c和b 會按照A的邊界進行定位，
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/Html4/loose.dtd">
<Html><HEAD><TITLE>CSS TEST</TITLE>
<style type=text/CSS>
body{
text-align: center;
background: #000;
}
#container{
width:778px;
background: #e3e3e3;
margin:0px auto;
}
#idParentDiv{
width:760px;
margin:0px auto;
text-align:left;
}
#boxleft{
width:200px;
height:80px;
background-color:yellow;
}
#boxmiddle{
float:left;
width:250px;
height:100px;
background-color:red;
}
#boxright{
width:250px;
height:120px;
background-color:blue;
}
</style>
<body>
<div id=container>
<div id=idParentDiv>
<div id=boxleft>boxleft---width:200px;height:20px;color:#FFFFFF;background-color:yellow;letter-spacing:0px; </div>
<div id=boxmiddle>boxmiddle---float:left;width:250px;height:30px;background-color:red;</div>
<div id=boxright>boxright----width:250px;height:50px;background-color:blue;</div>
</div>
</div>
</body>
</Html>