JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css">
<script src="https://code.jquery.com/jquery-3.2.1.slim.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.12.9/umd/popper.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
<div class="parent">
    <div class="child">
        <img src="" alt="" height="" width="">
    </div>
</div>

CSS

.parent {
  width: 300px;
  height: 300px;
  background: red
}
.child {
  width: 100px;
  height: 100px;
  background: green
}
.parent:hover .child {
  opacity: .5
}