<!DOCTYPE HTML>
<html class="focus-within">
<head>
<style>
    * {
        border: none;
    }
    .focus-within {
        border: 2px solid green;
    }
</style>
</head>
<body class="focus-within">
    <div class="focus-within">
        <input>
        <input>
        <input>
        <input class="focus-within">
        <input>
        <input>
        <input>
    </div>
    <script>
        let midInput = document.getElementsByTagName("input")[3];
        midInput.focus();
    </script>
</body>
</html>