HTML：如何将网页分为上下两个部分

1.使用table：

2.使用div+js：

<html>
    <head>
<style>body{margin:0;}</style>
<script>
function fixedDiv(){
    var d1 = document.getElementById("div1");
    var d2 = document.getElementById("div2");
    var h = window.document.body.clientHeight;
    d1.style.height=h*0.2;
    d2.style.height=h*0.8;
}
window.onload=function(){
    fixedDiv();
}
window.onresize=function(){
    fixedDiv();
}
</script>
    </head>
    <body>

<div id="div1" style="100%;overflow-y:auto;">
      <br>1<br>1<br>1<br>1<br>1<br>1<br>1<br>1<br>1<br>1<br>1<br>1<br>1<br>1
</div>
<div id="div2" style="100%;overflow-y:auto;">
      <br>1<br>1<br>1<br>1<br>1<br>1<br>1<br>1<br>1<br>1<br>1<br>1<br>1<br>1
      <br>1<br>1<br>1<br>1<br>1<br>1
</div>

    </body>
</html>

3.使用div+css：

//index.html
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>split</title>
<link rel="stylesheet" type="text/css" href="style.css" />
</head>
<body>
<div id="top"></div>
<div id="bottom">

</div>
</body>
</html>

//style.css

* {
margin:0;
padding:0;
}

#top {
background-color:yellow;
100%;
height:20%;
overflow:auto;
}

#bottom {
background-color:green;
100%;
height:80%;
overflow:auto;
}