JSFiddle - React, Tailwind, and code Playground

HTML

<div id="fb-pixel-outer">
  <iframe src="http://mainsubdomain.yoursite.com/track-conversion.html" id="fb-pixel-inner">    
  </iframe>
</div>

<!-- track-conversion.html should be a basic HTML page containing your Facebook Pixel code -->

CSS

/** Outer container, this prevents scrollbars from appearing due to iframe positioned outside of viewport **/
#fb-pixel-outer {
  overflow: hidden; 
  position: absolute; 
  top: 0px; 
  left: 0px;
}

/** this styling ensures that the iframe is miles outside of the viewport, and loaded by browser **/
#fb-pixel-inner {
  position: absolute;
  left: -9999px;
  top: -9999px;
  overflow: hidden;
  display: block;
  width: 1px; 
  height: 1px;
}