css样式这怎么填啊，🆘

img

<!doctype html>
<html lang="en">
<head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1" />
    <title> 页面名称 </title>
<style type="text/css">

.select2 em {
    background-color: green;
    color: blue;
}
#select1 + em {
    color: red;
}
</style>
</head>
<body>
    <div id="select1">
        <strong class="select2">
            <em>
                aaaaaaaaaaaaa
            </em>
        </strong>
    </div>
    <em>
        bbbbbbbbb
    </em>
</body>
</html>

img

第一个空
.select2 em{background-color:green;color:blue}

第二个空
em{color:red}

‘字体颜色为红色’这几个字再用一个容器包着，然后给这个容器color：red；’不能改变我的颜色‘就会还是绿色

    em:nth-child(1) {
        background-color: green;
        color: blue;
    }

    em:nth-child(2) {
        color: red;
    }