背景图片随鼠标滑动

<div class="testBefore"><h1>BEFORE</h1></div>
<div class="fixedBg"></div>
<div class="testAfter"><h1>AFTER</h1></div>
<style> 
        body,html{ height: 100%; }
        *{ margin: 0; padding: 0; }
        .fixedBg{ 
            min-height: 300px;
            background-image: url("https://www.supermap.com/pic/toppic/2018821121812QQ%E5%9B%BE%E7%89%8720180821121532.jpg"); 
            background-position: top center; 
            background-repeat: no-repeat; 
            background-attachment: fixed;
            background-size: cover; 
        }
        .testBefore,.testAfter{
            background: #333;
            width: 100%;
            height: 500px;
            text-align: center;
        }
        h1{
            color: #fff;
            font-size: 100px;
            line-height: 300px;
        }
</style>