<div class="accordion">
    <section class="accordion-item">
        <h1>Section 1</h1>
        <div class="accordion-item-content">
          <p>Content for section 1</p>
        </div>
    </section>
    <section class="accordion-item">
        <h1>Section 2</h1>
        <div class="accordion-item-content">
          <p>Content for section 2</p>
        </div>
    </section>
    <section  class="accordion-item accordion-item--default">
        <h1>Section 3</h1>
        <div class="accordion-item-content">
          <p>Content for section 3</p>
          <p>This is my default state.</p>
        </div>
    </section>
    <section class="accordion-item">
        <h1>Section 4</h1>
        <div class="accordion-item-content">
          <p>Content for section 4</p>
        </div>
    </section>
</div>

/* The Magic */
.accordion:hover .accordion-item:hover .accordion-item-content,
.accordion .accordion-item--default .accordion-item-content {
    height: 6em;
}

.accordion-item-content,
.accordion:hover .accordion-item-content {
    height: 0;
    overflow: hidden;
    transition: height .25s;
}

/* Aesthetic */
body {
  background: #222;
}

.accordion {
    padding: 0;
    margin: 0 auto;
    width: 20%;
    font-family: "PT Sans" sans-serif
}

.accordion .accordion-item {
  background-image: linear-gradient(90deg, #eee, #f5f5f5, #eee);
  border-bottom: 1px solid #666;
  padding: 1em;
  color: #eee;
}

.accordion h1 {
  margin: 0;
}

.accordion .accordion-item:nth-child(1) {
  background-color: hsl(200, 80%, 60%);
  background-image: linear-gradient(-90deg, hsl(200, 80%, 60%), hsl(200, 80%, 45%) 2em, hsl(200, 80%, 60%));

}

.accordion .accordion-item:nth-child(2) {
  background-color: hsl(280, 60%, 45%);
  background-image: linear-gradient(-90deg, hsl(280, 80%, 60%), hsl(280, 60%, 45%) 2em, hsl(280, 80%, 60%));
}

.accordion .accordion-item:nth-child(3) {
  background-color: hsl(40, 80%, 40%);
  background-image: linear-gradient(-90deg, hsl(40, 80%, 60%), hsl(40, 80%, 45%) 2em, hsl(40, 80%, 60%));
}

.accordion .accordion-item:nth-child(4) {
  background-color: hsl(80, 40%, 40%);
  background-image: linear-gradient(-90deg, hsl(80, 80%, 40%), hsl(80, 80%, 35%) 2em, hsl(80, 80%, 40%));
}