Smooth Vertical Accordion Menu With JavaScript And CSS3

A smooth vertical accordion menu created with JavaScript, CSS, CSS3 transitions, Font Awesome, and nested HTML lists.

JavaScript is used to toggle the CSS classes when expanding/collapsing accordion panels.

How to use it:

Create the accordion menu from nested lists as follows. It supports the unlimited number of levels.

<ul class="menu">
   <li class="list"><a href="#">JavaScript</a>
      <ul class="items">
         <li><a href="#"> Angular</a></li>
         <li><a href="#"> React</a></li>
         <li><a href="#"> Vue</a></li>
      </ul>
   </li>
   <li class="list"><a href="#">Adobe</a>
      <ul class="items">
         <li> <a href="#" > Photoshop</a></li>
         <li> <a href="#" > Illustrator</a></li>
         <li> <a href="#" > Dreamweaver</a></li>
      </ul>
   </li>
   <li class="list"><a href="#">Multi-Level</a>
      <ul class="items">
         <li> <a href="#" > Item 1-1 </a></li>
         <li> <a href="#" > Item 1-2 </a></li>
         <li class="list"><a href="#">List 1-1</a>
            <ul  class="items">
               <li> <a href="#" > Item 1-1-1</a></li>
               <li> <a href="#" > Item 1-1-2</a></li>
               <li class="list"><a href="#">List 1-2</a>
                  <ul  class="items">
                     <li> <a href="#" > Item 1-2-1</a></li>
                     <li> <a href="#" > Item 1-2-2</a></li>
                  </ul>
               </li>
            </ul>
         </li>
      </ul>
   </li>
</ul>

The necessary CSS/CSS3 rules for the accordion menu.

ul.menu {
  padding: 0;
  list-style: none;
  width: 400px;
  margin: 20px auto;
  font-family: 'Roboto';
  box-shadow: 0px 0px 25px #00000070;
  clear: both;
  display: table;
}
ul.menu .list {
  font-size: 14px;
  border-bottom: 1px solid #324252;
  position: relative;
  width: 100%;
  box-sizing: border-box;
  height: 50px;
  vertical-align: sub;
  background: #3e5165;
  clear: both;
}
ul.menu .list:after {
  content: "\f107";
  font-family: FontAwesome;
  position: absolute;
  right: 17px;
  top: 17px;
  padding: 0px 5px;
  color: #fff;
}
ul.menu .list:before {
  content: '\f07b';
  font-family: FontAwesome;
  position: absolute;
  left: 17px;
  top: 17px;
  padding: 0px 5px;
  color: #fff;
}
ul.menu .list a {
  text-decoration: none;
  color: #fff;
  padding: 17px 0px 17px 45px;
  display: block;
  height: 100%;
  box-sizing: border-box;
}
ul.menu .list a:hover {
  background-color: #324252;
  transition: 300ms all;
  color: #09fbd2;
}
ul.menu .list .items {
  height: 0px;
  overflow: hidden;
}
ul.menu .list .items a {
  padding: 17px;
}
ul.menu .list .items a:hover {
  background-color: #3f5d79;
  color: #fff;
  transition: 300ms all;
}
ul.menu .list:last-child {
  border-bottom: none;
}
ul.menu .active:after {
  content: "\f106";
  font-family: FontAwesome;
  position: absolute;
  right: 17px;
  top: 17px;
  padding: 0px 5px;
  color: #fff;
}
ul.menu .active:before {
  content: '\f07c';
  font-family: FontAwesome;
  position: absolute;
  left: 17px;
  top: 17px;
  padding: 0px 5px;
  color: #fff;
}
ul.menu .active > .items {
  display: block;
  background: #23313f;
  padding: 0px;
  height: auto;
  color: #fff;
  transition-timing-function: cubic-bezier(0.075, 0.82, 0.165, 1);
  transition: all 200ms;
  clear: both;
  float: left;
  width: 100%;
}
ul.menu .active > .items li {
  padding: 0px;
  border-bottom: 1px solid #324252;
  list-style: none;
}
ul.menu .active > .items li:last-child {
  border-color: transparent;
  padding-bottom: 0px;
}
ul.menu .active > .items .active > .items {
  background-color: #2f4b67;
}
ul.menu .active > a {
  color: #46efa4;
  text-transform: uppercase;
  font-weight: bold;
}
ul.menu .active .list {
  background: #697d92;
}
ul.menu .active .list a {
  padding: 17px 0px 17px 45px;
}

The main JavaScript to enable the accordion menu.

var list = document.querySelectorAll('.list');
function accordion(e) {
  e.stopPropagation();
  if (this.classList.contains('active')) {
      this.classList.remove('active');
  } else
  if (this.parentElement.parentElement.classList.contains('active')) {
      this.classList.add('active');
  } else
  {
      for (i = 0; i < list.length; i++) {
          list[i].classList.remove('active');
      }
      this.classList.add('active');
  }
}
for (i = 0; i < list.length; i++) {
  list[i].addEventListener('click', accordion);
}