(() => {
  //0. 获取元素
  const header = document.queryselector(".header");








  const en = document.queryselector(
    ".header_leftlanguage .header_leftlanguageen"
  );
  //1. 添加滚动事件，使header导航栏部分样式发生改变
  app.addeventlistener("scroll", () => {
    if (app.scrolltop > 0) {
      header.style.top = app.scrolltop + "px";
      header.classlist.remove("header__normal");
      header.classlist.add("header__active");
    } else {
      header.style.top = app.scrolltop + "px";
      header.classlist.remove("header__active");
      header.classlist.add("header__normal");
    }
  });








})();