nested accordion

HTML

<div class="collapsible">
    <h3><strong>Main#1</strong></h3>
  </div>
  <div class="content">
    <div class="collapsible">
      <h4>Sub#1</h4>
    </div>
    <div class="content">
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit</p>
    </div>
    <div class="collapsible">
      <h4>Sub#2</h4>
    </div>
    <div class="content">
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit</p>
    </div>
  </div>
  
  <div class="collapsible">
    <h3><strong>Main#2</strong></h3>
  </div>
  <div class="content">
    <div class="collapsible">
      <h4>Sub#1</h4>
    </div>
    <div class="content">
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit</p>
    </div>
    <div class="collapsible">
      <h4>Sub#2</h4>
    </div>
    <div class="content">
      <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit</p>
    </div>
  </div>

CSS

.collapsible {
  background-color: white;
  color: var(--lowesBlue);
  cursor: pointer;
  padding: 1vw;
  width:97%;
  height: 60px;
  max-height: 100%;
  margin: 5px 10px 5px 10px;
  border: 2px solid black;
  text-align: left;
  outline: none;
  font-size: 25px;
}

.content {
  padding: 0 18px;
  max-height: 0;
  overflow: hidden;
  background-color: white;
  transition: max-height 0.2s ease-out;
}

h3{
  display:inline-block;
  vertical-align: middle;
}

h4{
  display:inline-block;
  vertical-align: middle;
  font-size: 22px;
}

JavaScript

$(function() {
  var coll = document.getElementsByClassName("collapsible");

  //setting buttons of class 'collapsible' to extend on click
  for (i = 0; i < coll.length; i++) {
    coll[i].addEventListener("click", function () {
      this.classList.toggle("active");
      var content = this.nextElementSibling;
      if (content.style.maxHeight) {
        content.style.maxHeight = null;
      } else {
          content.style.maxHeight = content.scrollHeight + "px";
      }
    });
  }
});