neptune/core/static/modal.js

// var modal = document.querySelector('.modal');  // assuming you have only 1
var modal = document.getElementById("drilldown-modal");
var html = document.querySelector('html');

var elements = document.querySelectorAll('.modal-background');
for(var i = 0; i < elements.length; i++) {
    elements[i].addEventListener('click', function(e) {
      // elements[i].preventDefault();
      modal.classList.remove('is-active');
      html.classList.remove('is-clipped');
    });
}

var elements = document.querySelectorAll('.modal-close');
for(var i = 0; i < elements.length; i++) {
    elements[i].addEventListener('click', function(e) {
      // elements[i].preventDefault();
      modal.classList.remove('is-active');
      html.classList.remove('is-clipped');
    });
}

function activateButtons() {
  var elements = document.querySelectorAll('.modal-close-button');
  for(var i = 0; i < elements.length; i++) {
      elements[i].addEventListener('click', function(e) {
        // elements[i].preventDefault();
        modal.classList.remove('is-active');
        html.classList.remove('is-clipped');
      });
  }
}
activateButtons();
// modal.querySelector('.modal-close-button').addEventListener('click', function(e) {
//   e.preventDefault();
//   modal.classList.remove('is-active');
//   html.classList.remove('is-clipped');
// });