var modal = document.querySelector('.modal');  // assuming you have only 1
var html = document.querySelector('html');
modal.querySelector('.modal-background').addEventListener('click', function(e) {
  e.preventDefault();
  modal.classList.remove('is-active');
  html.classList.remove('is-clipped');
});
modal.querySelector('.modal-close').addEventListener('click', function(e) {
  e.preventDefault();
  modal.classList.remove('is-active');
  html.classList.remove('is-clipped');
});
modal.querySelector('.modal-close-button').addEventListener('click', function(e) {
  e.preventDefault();
  modal.classList.remove('is-active');
  html.classList.remove('is-clipped');
});