8.2 z-index兄弟元素同时开启定位方案兄弟元素堆叠顺序谁的z-index高谁的优先级高//

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<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        div{
            width: 100px;
            height: 100px;
        }
        .div1{
            background-color: yellow;
            position: relative;
            z-index: -1;
        }
        .div2{
            background-color: red;
            margin-left: 50px;
            margin-top: -50px;
            position: relative;
        }
    </style>
</head>
<body>
    <!-- 兄弟元素 同时开启定位方案 
        兄弟元素堆叠顺序 谁的z-index高 谁的优先级高
    -->
    <div class="div1"></div>
    <div class="div2"></div>
</body>
</html>