who.html

<div class="ghostDropBlock">
  <span>Drop here to target this display option with this audience segment.</span>
</div>

who.import.less

.ghostDropBlock {
  display: block;
  min-height: 200px;
  border: 3px dashed @gray_color;
  padding: 50px;
  text-align: center;
  color: @gray_color;
}