Vladimir166

- var element = document.getElementById('portfolio-content-nav') + window.pageYOffset + 'px';
+ var element = document.getElementById('portfolio-content-nav');
window.addEventListener('scroll', function () {
-   if (element > 100) {
+   if (window.scrollY > 100) {
        element.classList.add("shadow");
    } else {
        element.classList.remove("shadow");
    }
});