document.addEventListener("DOMContentLoaded", function () {
  (function Navbar() {
    const menuButton: HTMLAnchorElement = document.getElementById('menu-button') as HTMLAnchorElement;
    const navMenu: HTMLDivElement = document.getElementById('nav-menu') as HTMLDivElement;

    menuButton.onclick = (event) => {
      navMenu.classList.toggle('is-active');
    }


  })();
  //....
});