<ul class="list" aria-live="assertive">
        <li class="list-container show" >
            <div class="list-item show">List Item</div>
        </li>
        <li class="list-container show">
            <div class="list-item show">List Item</div>
        </li>
        <li class="list-container show" >
            <div class="list-item show">List Item</div>
        </li>
        <li class="list-container show" >
            <div class="list-item show">List Item</div>
        </li>
    </ul>
<button class="add-btn">Add New Item</button>

*{
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: Arial, Helvetica, sans-serif;
    line-height: 1.2;
}
body{
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    padding: 1rem;
}
.list{
    list-style: none;
}

.list-container{
    list-style: none;
    text-align: center;
    font-size: 3.5rem;
    width: 300px;
    height: 0;
    position: relative;
    cursor: pointer;
    overflow: hidden;
}
.list-container.show:not(:first-child){
  margin-top: 10px;
}
.list-container .list-item{
    padding: 2rem 0;
    width: 100%;
    background-color: lightgray;
    position: absolute;
    opacity: 0;
    top: 0;
    left: 0;
    transition: all 0.6s ease-out;
}
.list-container .list-item.show{
    opacity: 1;
}
.add-btn{
    background-color: transparent;
    border: 1px solid black;
    margin-top: 10px;
    width: 300px;
    text-align: center;
    cursor: pointer;
    padding: 2rem 0;
    font-size: 2.5rem;
}

const addBtn = document.querySelector('.add-btn');
const list = document.querySelector('.list');

const listItems = document.querySelectorAll('.list-item');
function calculateHeightOfListContainer(){
    const firstListItem = listItems[0];
    let heightOfListItem = firstListItem.clientHeight;
    const styleTag = document.createElement('style');
    document.body.prepend(styleTag);
    styleTag.innerHTML = `.list-container.show {
        height: ${heightOfListItem}px;
    }`;
    setTimeout(function(){
        styleTag.innerHTML += `.list-container {
            transition: all 0.6s ease-out;
        }`;
    }, 0);
};
calculateHeightOfListContainer();

function removeListItem(e){
    let container = e.target;
    while(!container.classList.contains('list-container')){
        container = container.parentElement;
    }
    container.classList.remove('show');
    const listItem = container.querySelector('.list-item');
    listItem.classList.remove('show');
    container.ontransitionend = function(){
      container.remove();
    }
}

//DOCUMENT LOAD
document.querySelectorAll('.list .list-container').forEach(function(container) {
    container.onclick = removeListItem;
});

addBtn.onclick = function(e){
    const container = document.createElement('li'); container.classList.add('list-container'); container.setAttribute('role', 'listitem');
    const listItem = document.createElement('div'); listItem.classList.add('list-item'); listItem.innerHTML = 'List Item';
    container.append(listItem);
    addBtn.parentNode.insertBefore(container, addBtn);
    container.onclick = removeListItem;
    setTimeout(function(){
        container.classList.add('show'); listItem.classList.add('show');
    }, 15);
}