老师您好，z-index是不是只能在position属性为relative时候才能用？

来源：2-7 编程练习

键盘上的莫扎特

2019-05-09 13:44:01

<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title>Document</title>
    <style>
    *{
        padding: 0;
        margin: 0;
    }
        .blue{
            width: 100px;
            height: 100px;
            background: blue;
            position:relative;
            top:50px;
            left:50px;
            z-index:2;

        }
        .red{
            width: 100px;
            height: 100px;
            background: red;
            position:relative;
            z-index: 1;
        }
    </style>
</head>
<body>
    <div class="blue"></div>
    <div class="red"></div>
</body>
</html>