Open modal using JavaScript (not jQuery)

I’m trying to repurpose some code I obtained from Codepen. It’s written using jQuery but I want to rewrite the script using JavaScript.

The original codepen (see: Codepen) shows a few ways to open a modal window using animation. I’m using the ‘UNFOLDING’ animation.

The Codepen uses the following jQuery:

$('.button').click(function(){
   var buttonId = $(this).attr('id');
   $('#modal-container').removeAttr('class').addClass(buttonId);
   $('body').addClass('modal-active');
})

$('#modal-container').click(function(){
   $(this).addClass('out');
   $('body').removeClass('modal-active');
});

I’m trying to rewrite this as JavaScript.

I’ve got the modal to open with the following JavaScript:

let button = document.getElementById('start');
let body = document.body;
button.addEventListener('click', () => {
   document.getElementById('modal-container').classList.add('one');
   body.classList.add("modal-active");
});

BUT, I can’t get it to close!

I tried the following but it doesn’t work properly (compared to original Codepen):

let button2 = document.getElementById('modal-container');
button2.addEventListener('click', () => {
   document.getElementById('modal-container').classList.add('out');
   document.getElementById('modal-container').classList.remove('one');
   body.classList.remove("modal-active");
});

Hoping someone can show me where I’ve gone wrong.

Thanks.