document.addEventListener("scroll", function () {
    let s = document.body.scrollTop || document.documentElement.scrollTop;    
    let backtop = document.querySelector(".backtop");
    if (s > 500) {
        backtop?.classList.add("active");
        backtop?.addEventListener("click", function () {
            document.querySelector("body")?.scrollIntoView({
                behavior: "smooth",
            });
        });
    } else {
        backtop?.classList.remove("active");
    }
});