<body>
  <div id="container">
    <h1>See change in this line</h1>
    <p>Hover over this line</p>
  </div>
</body>
<script src="https://rouninmedia.github.io/axe/axe.js"></script>

* {
  margin: 0;
  left: 0;
  top: 0;
  cursor: pointer;
}
body {
  display: flex;
  flex-direction: column;
  justify-content: center;
  place-items: center;
  height: 100vh;
  width: 100vw;
  background: rgba(55, 53, 64, .4);
}
#container {
  width: 400px;
  height: 150px;
  border-radius: 10px;
  background: #373540;
  box-shadow: 0px 5px 100px              rgba(0,0,0,.5);
}
p, h1 {
  margin: 30px auto;
  font-size: 20px;
  color: white;
  text-align: center;
}
p:hover ? h1 {
  font-size: 30px;
  color: red;
}

External CSS

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External JavaScript

This Pen doesn't use any external JavaScript resources.