JSFiddle - React, Tailwind, and code Playground

HTML

<div id="gallerySlider">
  <div class="placeholder">
    <img src="http://www.graphic-buffet.com/wp-content/uploads/2012/04/cloud-example.jpg">
  </div>	
</div>

CSS

img {
  width:300px;
  position:relative;
}

.placeholder  {
 position:relative;
}
#gallerySlider .placeholder::after {
display:block;
content: "<div class='placeholder'>▶️</div>";
position: absolute;
z-index: 100;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);
}