代码：
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" lang="en">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
<title>t4</title>
<style>
* {
margin: 0px;
padding: 0px;
}
#div1 {
width: 100px;
height: 100px;
border: 1px solid black;
background-color: red;
float: left;
}
#div2 {
width: 100px;
height: 100px;
border: 1px solid black;
background-color: yellow;
float:left;
}
#div3 {
width: 100px;
height: 100px;
border: 1px solid black;
background-color: blue;
position:relative;/*absolute*/
top:100px;
}
</style>
</head>
<body>
<div id="div1">1111111111</div>
<div id="div2">2222222222</div>
<div id="div3">3333333333</div>
</body>
</html>
