左侧定宽右侧自适应布局

<!DOCTYPE html>
<html lang="en">

<head>
<meta charset="UTF-8">
<title>Document</title>
<style>
* {
margin: 0;
padding: 0;
}

.left {
float: left;
width: 200px;
height: 200px;
background-color: red;
}

.right {
margin-left: 200px;
height: 200px;
background-color: green;
}
</style>
</head>

</html>