window.onscroll = () => { scrollFunction() };
window.onload = () => { scrollFunction() };

function scrollFunction() {
    let nav = document.querySelector("nav");
    // let scrollHeight = window.innerHeight - nav.offsetHeight;
    let scrollHeight = 0;

    if (document.body.scrollTop > scrollHeight ||
        document.documentElement.scrollTop > scrollHeight) {
        nav.classList.add("scrolled");
    } else {
        nav.classList.remove("scrolled");
    }
}