JSFiddle - React, Tailwind, and code Playground

HTML

<div class="bluebox">
  <img src="http://i.imgur.com/qxvPxFX.png">
</div>
<div class="redbox">
  <img src="http://i.imgur.com/q6VSm7U.png">
</div>

CSS

.redbox img{
  width:30%;
  height:auto;
  position:absolute;
  top:0;
}
.bluebox img{
  /*Make this image fit exactly inside the redbox. The redbox borders are 10 IMAGE PIXELS wide (but have a variable width in reality, since the window is scalable.)*/
  position:absolute;
  z-index:1;
  left:???;
  top:???;
  width:???;
  height:auto;
}