Viacheslav Popov

const { classList: cl } = document.querySelector('#overlay');
const activeMenuClass = 'show-menu';
const matches = (el, ...selectors) => selectors.some(n => el.matches(n));

document.addEventListener('click', ({ target: t }) => {
  if (matches(t, '#close-menu', 'li > a')) {
    cl.remove(activeMenuClass);
  } else if (matches(t, '#open-menu')) {
    cl.add(activeMenuClass);
  }
});