scroll

let lastScrollTop = 0;
gnb = document.getElementById('gnb');
window.addEventListener("scroll", function(){
    let scrollTop = window.pageYOffset || document.documentElement.scrollTop;
    if(scrollTop > lastScrollTop){
        gnb.classList.add('active');
    } else {
        gnb.classList.remove('active');
    }
    lastScrollTop = scrollTop;
})