<!DOCTYPE HTML>
<html>
<head>
<style>
    * {
        border: none;
    }
    :focus-within {
        border: 2px solid green;
    }
</style>
</head>
<body>
    <div>
        <input form="form" id="input" autofocus>
    </div>
    <div>
        Foo
    </div>
    <div>
        Bar
    </div>
</body>
</html>