<h3>背景あり</h3>
<div class="fa-3x">
  <i class="fab fa-amazon bgc" data-fa-transform="shrink-6" data-fa-mask="fas fa-circle"></i>
  <i class="fas fa-pencil-alt bgc" data-fa-transform="shrink-10 up-.5" data-fa-mask="fas fa-comment"></i>
  <i class="fab fa-facebook-f bgc" data-fa-transform="shrink-3.5 down-1.6 right-1.25" data-fa-mask="fas fa-circle"></i>
  <i class="fas fa-headphones bgc" data-fa-transform="shrink-6" data-fa-mask="fas fa-square"></i>
</div>

<h3>背景なし</h3>
<div class="fa-3x">
  <i class="fab fa-amazon" data-fa-transform="shrink-6" data-fa-mask="fas fa-circle"></i>
  <i class="fas fa-pencil-alt" data-fa-transform="shrink-10 up-.5" data-fa-mask="fas fa-comment"></i>
  <i class="fab fa-facebook-f" data-fa-transform="shrink-3.5 down-1.6 right-1.25" data-fa-mask="fas fa-circle"></i>
  <i class="fas fa-headphones " data-fa-transform="shrink-6" data-fa-mask="fas fa-square"></i>
</div>

h3 {
  border-bottom: 1px solid #000;
}
.bgc {
  background-color: MistyRose;
}