My solution to the challenge... Perhaps someone could review?

I think your comments are very easy to understand! I also think the way you checked for previousElementSiblings was very clever. If you wanted the code to be more 'elegant' I would recommend writing a function to test if an li element is the first and/or last element and adjust the buttons accordingly. Then you can call the function whenever the list changes. You can see my function here:

const toggleLiButtons = (ul) => {
  for(let i=0; i<ul.children.length; i++){
    let li = ul.children[i];
    let up = li.querySelector('button.up');
    let down = li.querySelector('button.down');
    if(li.isSameNode(listUL.firstElementChild)) {
      up.style.display = 'none';
    } else {
      up.style.display = 'block'; 
    }
    if(li.isSameNode(listUL.lastElementChild)) {
      down.style.display = 'none';
    }  else {
     down.style.display ='block';
    }
  }
}

I just declare it right after the attachListItemButtons function and then I just call it like

toggleLiButtons(listUl)

when I create the initial list and inside the event handlers for adding an item, removing an item, or moving an item up or down. That way you don't have to write similar checks and button removals for each different possibility throughout the code.

Emmie Cole I really like your solution, though when I try to implement it, first item's buttons are differently alligned than the rest - they 'stick' to the text content of the first li (left). Any ideas why?