等高佈局，利用css maigin 和 padding-bottom屬性：先將元素的內邊距向外，再將元素的外邊距設爲負值，最後將父元素的設置爲overflow：hidden
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Document</title>
<style>
*{
margin: 0;
padding: 0;
}
.header, .footer{
height: 20px;
text-align: center;
border:1px solid deeppink;
background-color: deepskyblue;
}
.content .left{
position: relative;
left: -200px;
float: left;
width: 200px;
background-color: yellow;
margin-left: -100%;
}
.content .right{
position: relative;
float: left;
right: -200px;
width:200px;
background-color: yellow;
margin-left: -200px;
}
.content .middle{
float: left;
background-color: blue;
width:100%;
}
.clearfix{
/* //清除浮動 */
*zoom: 1;
}
.clearfix:after{
content:"";
display: block;
clear: both;
}
.content{
padding: 0 200px;
overflow: hidden;
}
/* 等高佈局 */
.content .middle , .content .left , .content .right{
padding-bottom: 1000px;
margin-bottom: -1000px;
}
</style>
</head>
<body>
<!-- 兩邊固定，中間自適應 -->
<!-- 當中列要完整顯示 -->
<!-- 當中列要優先加載 -->
<div class="header">header</div>
<div class="content clearfix" >
<div class="middle">
middle <br>
middle <br>
middle <br>
middle <br>
middle <br>
</div>
<div class="left">
left <br >
left <br >
left <br >
</div>
<div class="right">
right <br>
right <br>
right <br>
right <br>
right <br>
right <br>
right <br>
right <br>
right <br>
right <br>
</div>
</div>
<div class="footer">footer</div>
</body>
</html>