window.addEventListener("scroll", function (){
	var header = document.querySelector("header");
	header.classList.toggle("header-scroll", window.scrollY>50);
});

var scrollTopPrev = window.pageYOffset;
window.onscroll = function () {
    var currentScrollpos = window.pageYOffset;
    if (scrollTopPrev > currentScrollpos) {
        document.querySelector("header").style.top = "0";
    } else {
        document.querySelector("header").style.top = "-100px";
    }

    scrollTopPrev = currentScrollpos;
};