JSFiddle - React, Tailwind, and code Playground

HTML

<div class="class_a">
  <div>Class A</div>
        <div class="class_b">
          Class B
        </div>
</div>

CSS

.class_a {
  background:#333;
 
  color:#fff
}
.class_a div {
   width:100px;
  height:100px;
}
.class_b {
  background:#000;
  width:100px;
  height:100px;
  color:#fff
}

.class_a:hover .class_b {background:green}