<label for="trigger">Toggle box</label>
<div>
    OTHER HTML CONTENT
</div>
<input id="trigger" type="checkbox">
<div class="box">
  SHOW / HIDE BOX
</div>

.box {
  display: none;
  background: #ccc;
  width: 200px;
  height: 100px;
}

#trigger {
  display: none;
}

#trigger:checked + .box {
  display: block;
}