function onKonamiCode(callback) {
  let input = "";
  const konami =
    "arrowuparrowuparrowdownarrowdownarrowleftarrowrightarrowleftarrowrightba";
  document.addEventListener("keydown", (e) => {
    input = (input + e.key.toLowerCase()).slice(-konami.length);
    if (input === konami) callback();
  });
}

onKonamiCode(() => {
  const body = document.body;
  const header = document.getElementById("header");

  if (body.style.backgroundColor === "white") {
    body.style.backgroundColor = "black";
    header.style.color = "white";
  } else {
    body.style.backgroundColor = "white";
    header.style.color = "black";
  }
});