Smooth Vertical Accordion Panels with Pure JS and CSS3

Preview:

Description:

A pure JavaScript/HTML5/CSS approach to create a vertical accordion with smooth sliding effects based on CSS3 transitions.

How to use it:

Create the Html structure for the accordion.

<section class="accordion">
  <article class="accordion-panel">
    <a class="accordion-panel__heading" href="javascript:;">Accordion Panel One</a>
    <div class="accordion-panel__content">
      <h4>Title One</h4>
      <p>Description One</p>
    </div>
  </article>
  <article class="accordion-panel">
    <a class="accordion-panel__heading" href="javascript:;">Accordion Panel Two</a>
    <div class="accordion-panel__content">
      <h4>Title Two</h4>
      <p>Description Two</p>
    </div>
  </article>
  <article class="accordion-panel">
    <a class="accordion-panel__heading" href="javascript:;">Accordion Panel Three</a>
    <div class="accordion-panel__content">
      <h4>Title Three</h4>
      <p>Description Three</p>
    </div>
  </article>
  ...
</section>

Style the accordion in the CSS.

.accordion {
  border-radius: 3px;
  overflow: hidden;
  border: 3px solid #6495ED;
}
.accordion-panel {
  border: 0px #6495ED solid;
  transition: all .6s .2s ease;
}
.accordion-panel.active {
  transition: all .2s .6s;
  border-left: 15px #6495ED solid;
}
.accordion-panel__heading {
  padding: 20px;
  display: block;
  text-decoration: none;
  text-transform: uppercase;
  letter-spacing: 2px;
  color: #6495ED;
  background: #f5f5f5;
  font-family: 'Source Sans Pro', sans-serif;
  font-size: 12px;
  font-weight: 600;
  border-bottom: 1px solid #6495ED;
  transition: all .6s;
  cursor: pointer;
}
.accordion-panel__heading:HOVER {
  color: #333;
  background: #f1f1f1;
  transition: all .2s;
}
.active .accordion-panel__heading:HOVER,
.active .accordion-panel__heading {
  color: #333;
  background: #fff;
  border-bottom: 0;
}
.accordion-panel__content {
  padding: 0 20px 0 20px;
  background: #f1f1f1;
  max-height: 0;
  overflow: hidden;
  transition: all .6s;
}
.active .accordion-panel__content {
  max-height: 500px;
  padding: 0 20px 20px 20px;
  background: #fff;
}

The JavaScript to enable the accordion. Include the myAPP.js directly into your document.

<script src="myAPP.js"></script>

Changelog:

06/25/2018

• Use Element.classList