为什么first-child无效，在其他文件单独测试没问题，这是什么原因


<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>

    <style>
        * {
            padding: 0px;
            margin: 0px;
            box-sizing: border-box;
        }

        ol {
            list-style: none;
            display: flex;
            flex-wrap: nowrap;
            background-color: aqua;
            
        }

        .one a{
            white-space: nowrap;
        }

       ol:first-child{
            flex-grow: 1;
            flex-wrap: wrap;
            background-color: blueviolet;
        }

        body {
            display: flex;
            justify-content: center;
        }

        main {
            display: flex;
            width: 80vw;
           
            background-color: antiquewhite;
        }
        div:first-child{
            background-color: red;
        }
    </style>
</head>

<body>
    <main>
        <a href="">logo</a>
        <ol class="one">
            <li><a href="">奔驰</a></li>
            <li><a href="">奥迪</a></li>
            <li><a href="">雷克萨斯</a></li>
            <li><a href="">宝马</a></li>
        </ol>
        <ol>
            <li><a href="">购买</a></li>
            <li><a href="">注册</a></li>
        </ol>
        <div>1</div>
        <div>1</div>
        <div>1</div>
        <div>1</div>
    </main>
</body>

</html>