JSFiddle - React, Tailwind, and code Playground

HTML

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

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

CSS

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

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

.class_a:hover ~ .class_b {background:green}