Auto-Height a responsive menu

Question

I'm trying to make a mobile menu with the structure of ul > li > ul which each sub ul having its height based of the number of li.

But when entering a sub-sub tiny ul of a big sub ul makes the sub-sub tiny ul overflow vertically which is showing the content of its parent :

How can I prevent the sub-sub tiny ul to be overflow vertically ?

$(document).ready(function(){
  let menu = $('nav')
  
  // open submenu
  menu.find('a').on('click', function(){
    let parent = $(this).parent()
    parent.toggleClass('active')
  })
  
  // close submenu
  menu.find('.back').on('click', function(){
    let parent = $(this).parent().parent()
    parent.toggleClass('active')
  })
})

:root {
  font-size: 10px;
}

* {
  box-sizing: border-box;
}

nav {
  position: fixed;
  width: 300px;
  box-shadow: 0 0 5px rgba(0, 0, 0, .2);
  overflow: hidden;
}

nav a:hover {
  color: blue;
}

nav > ul {
  height: auto;
}

ul {
  list-style: none;
  padding-inline-start: 0;
  padding: 0 1.5rem;
  margin: 0;
  width: 100%;
  background: #FFF;
}

ul > li:not(:last-child) {
  border-bottom: 1px solid #AAA;
}

ul > li > a {
  display: flex;
  justify-content: space-between;
  
  padding: 1.2rem 1.5rem;
  font-size: 1.5rem;
  line-height: 1.5em;
  font-weight: bold;
  text-transform: uppercase;
  font-family: sans-serif;
  cursor: pointer;
}

ul > li:not(.back) > ul ~ a::after {
  content: '►';
}

ul > li > ul {
  position: absolute;
  top: 0;
  left: 0;
  transform: translateX(100%);
  transition: .3s;
  overflow-x: hidden;
  z-index: 2;
  height: 100%;
}

ul > li.back {
  margin: 0 -1.5rem;
  border-bottom-width: 0;
  z-index: 1;
}

ul > li.back > a {
  background: #DDD;
  font-size: 1rem;
  justify-content: flex-start;
}

ul > li.back > a::before {
  content: '◄';
  margin-right: .5rem;
}

ul > li.see-all > a {
  padding: .5rem 0;
  font-size: 1.3rem;
  text-align: center;
  text-transform: inherit;
  justify-content: center;
}

ul > li.active > ul {
  transform: translateX(0);
}

ul.dark {
  padding: 0;
}

ul.dark > li:not(:last-child) {
  border-bottom: 1px solid #FFF;
}

ul.dark > li > a {
  background: #AAA;
  padding: 1.5rem 3rem;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<nav>
  <ul>
    <li>
      <ul>
        <li class="back">
          <a>Return</a>
        </li>
        <li>
          <ul>
            <li class="back">
              <a>Return</a>
            </li>
            <li>
              <ul>
                <li class="back">
                  <a>Return</a>
                </li>
                <li>
                  <a>Sub-sub-category 1</a>
                </li>
                <li>
                  <a>Sub-sub-category 2</a>
                </li>
              </ul>
              <a>Sub-category 1</a>
            </li>
            <li>
              <a>Sub-category 2</a>
            </li>
            <li>
              <a>Sub-category 3</a>
            </li>
            <li>
              <a>Sub-category 4</a>
            </li>
            <li>
              <a>Sub-category 5</a>
            </li>
          </ul>
          <a>Category 1</a>
        </li>
        <li>
          <a>Category 2</a>
        </li>
        <li>
          <a>Category 3</a>
        </li>
        <li class="see-all">
          <a>See all products</a>
        </li>
      </ul>
      <a>Products</a>
    </li>
    <li>
      <ul>
        <li class="back">
          <a>Return</a>
        </li>
        <li>
          <a>Fiesta</a>
        </li>
      </ul>
      <a>Events</a>
    </li>
  </ul>
  <ul class="dark">
    <li>
      <a>Stores</a>
    </li>
    <li>
      <a>Account</a>
    </li>
    <li>
      <a>Contact</a>
    </li>
  </ul>
</nav>

Thanks for feeback