position 固定的属性，是全局的。和DIV层次无关。
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<div style="background-color: aqua">标记1</div>
<div style="background-color: brown ;position: fixed;
bottom: 0;right: 0" >标记2</div>
</body>
</html>
结果如下：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<div style="background-color: aqua ;height: 100px">
标记1
<div style="background-color: brown ;"
>标记2</div>
</div>
</body>
</html>
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Title</title>
</head>
<body>
<div style="background-color: aqua ;height: 100px">
标记1
<div style="background-color: brown ;position: fixed;right: 0;bottom: 0;"
>标记2</div>
</div>
</body>
</html>