求解决：section标签里的样式如何生效？

如下图代码，但颜色效果没有出来，只有div的尺寸，求帮助

img

img


```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>

伪类中间没有空格
section div:nth-child(1) {
background-color:pink;
}
section div:nth-child(2) {
background-color: plum;
}

div多了个空格

<!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>