如下图代码，但颜色效果没有出来，只有div的尺寸，求帮助
```css
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>流式布局（百分比布局）</title>
<style>
section{
width:100%;
}
section div {
width: 100%;
height: 400px;
}
section div :nth-child(1) {
background-color:pink;
}
section div :nth-child(2) {
background-color: plum;
}
</style>
</head>
<body>
<section>
<div>布局1</div>
<div>布局2</div>
</section>
</body>
</html>
