<button class="button">Toggle Hidden Element</button>

<div class="element"></div>

<script src="https://code.jquery.com/jquery-2.2.4.min.js"></script>

<script>
$('.button').on('click',function(){
  $('.element').show().focus().toggleClass('active');
});
</script>
.button {
  background-color: #eee;
  border: 0px;
  padding: 10px;
  border-radius: 5px;
}

.element { 
  opacity: 0;
  display: none;
  transition: opacity .2s linear;
  margin-top: 20px;
  background-color: #CC333F;
  width: 50px;
  height: 50px;
}

.element.active { 
  opacity: 1;
}

External CSS

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External JavaScript

This Pen doesn't use any external JavaScript resources.