probably many ways to do it, but i'd do this:
Code:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<style>
#box {
background-color: green;
width: 200px;
height: 200px;
border: 3px solid white;
}
#boxContainer {
border: 1px solid red;
width: 206px;
}
</style>
</head>
<body>
<div id="boxContainer">
<div id="box">
</div>
</div>
</body>
</html>