Layout-2相关代码:3列布局代码演化[一]

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>无标题文档</title>
<style type="text/css">
.right,.left{height:300px;200px;}
.right{ float:right;background:#000000;}
.left{ float:left;background:#009933;}
.main{background:#F60; height:300px;}
</style>
</head>
<body>
<div class="right">RIGHT</div>
<div class="left">LEFT</div>
<div class="main">MAIN</div>    
</body>
</html>

代码演化2:

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>无标题文档</title>
<style type="text/css">
.right, .left {
	height: 300px;
	 200px;
}
.right {
	float: right;
	background: #000000;
	margin-right:10%;
}
.left {
	float: left;
	background: #009933;
	margin-left:10%;
}
.main {
	background: #F60;
	height: 300px;
	margin:0 10%;
}
</style>
</head>
<body>
  <div class="right">RIGHT</div>
  <div class="left">LEFT</div>
  <div class="main">MAIN</div>
</body>
</html>

代码演化3:

<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>无标题文档</title>
<style type="text/css">
#outbox {
	 80%;
	margin-right: auto;
	margin-left: auto;
	min-500px;
}
.right, .left {
	height: 300px;
	 200px;
}
.right {
	float: right;
	background: #000000;
}
.left {
	float: left;
	background: #009933;
}
.main {
	background: #F60;
	height: 300px;
}

</style>
</head>
<body>
<div id="outbox">
  <div class="right">RIGHT</div>
  <div class="left">LEFT</div>
  <div class="main">MAIN</div>
</div>
</body>
</html>

代码演化4：

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>Layout</title>
<style type="text/css">
* {
	margin: 0;
	padding: 0;
}
body {
	position: relative;
}
.right, .left {
	height: 300px;
	 200px;
	z-index: 2;
}
.right {
	position: absolute;
	right: 0;
	top: 0;
	background: #000000;
}
.left {
	position: absolute;
	left: 0;
	top: 0;
	background: #009933;
}
.main {
	margin-right: 200px;
	background: #F60;
	height: 300px;
	margin-left: 200px;
}
</style>
</head>
<body>
<div class="main">main</div>
<div class="left">LEFT</div>
<div class="right">RIGHT</div>
</body>
</html>

回答问题:

请分别说出上面的这种布局的主要特点.