function hide(element) {
  element.classList.add("hidden");
}
function unhide(element) {
  element.classList.remove("hidden");
}

function toggle_all_header_links() {
  const headerLinks = document.querySelector("header > .links");
  const button_link = document.querySelector("header > button");
  headerLinks.classList.toggle("display_links");
  button_link.textContent = headerLinks.classList.contains("display_links")
    ? "▲"
    : "▼";
}