Алексей Королёв

чекбокс.addEventListener('change', e => кнопка.disabled = !e.target.checked);

let header = document.getElementById("nav");

window.addEventListener("scroll", () => {
  let scrollPosition = window.pageYOffset;
  if (scrollPosition > 150) header.classList.remove("header_fix");
  else if (scrollPosition < 150) header.classList.add("header_fix");
});

.xfieldimagegallery {
    margin: 0;
    padding: 0;
    list-style: none;
    clear: both;
    display: flex;
    overflow: auto;

.xfieldimagegallery li img {
    display: block;
    border-radius: 10px;
    height: 130px;
    transition: box-shadow 0.5s ease;