另一个可折叠部分中的可折叠部分不会充分展开

var coll = document.getElementsByClassName("collapsible");
var i;

for (i = 0; i < coll.length; i++) {
  coll[i].addEventListener("click", function() {
    this.classList.toggle("active");
// managed by css
    var content = this.nextElementSibling;
    if (content.style.maxHeight){
      content.style.maxHeight = null;
    } else {
      content.style.maxHeight = content.scrollHeight + "px";
      content.parentNode.style.maxHeight = (parseInt(content.parentNode.style.maxHeight) + content.scrollHeight) + "px";
    } 
  });
  coll[i].nextElementSibling.addEventListener("transitionend", function()
  {
      this.parentNode.style.maxHeight = this.parentNode.scrollHeight + "px";
  });
}

.collapsible {
  background-color: #2d2e2e;
  color: white;
  cursor: pointer;
  padding: 10px;
  width: 100%;
  border: none;
  text-align: left;
  outline: none;
  font-size: 15px;
}

.active, .collapsible:hover {
  background-color: black;
}

.collapsible:after {
  content: '\002B';
  color: white;
  font-weight: bold;
  float: left;
  margin-right: 5px;
}

.active:after {
  content: "\2212";
}

.collapse_content {
  padding: 0 18px;
  max-height: 0;
  overflow: hidden;
  transition: max-height 0.1s ease-out;
}

<button class="collapsible">Full Collapsible Set:</button>
<div class="collapse_content">
  <button class="collapsible">Open Section 1</button>
  <div class="collapse_content">
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
  </div>
  <button class="collapsible">Open Section 2</button>
  <div class="collapse_content">
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco.</p>
  </div>
  <button class="collapsible">Open Section 3</button>
  <div class="collapse_content">
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.</p>
  </div>
</div>