Well played:

    <script>
    document.getElementById("bonus").innerHTML = 'body { font-family: "Comic Sans MS", "Chalkboard SE", "Comic Neue", cursive, sans-serif; }'
    window.onscroll = function() {
    document.getElementById("bonus").innerHTML = 'body { font-family: serif; }'
    window.onscroll = null
    }
    </script>