<body>
  <div id="container">
    <h1>Hover over this line</h1>
     <h2>No change in this line</h2>
    <p>See change in this line</p>
  </div>
</body>

* {
  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: 200px;
  border-radius: 10px;
  background: #373540;
  box-shadow: 0px 5px 100px              rgba(0,0,0,.5);
}
p, h1, h2 {
  margin: 30px auto;
  font-size: 20px;
  color: white;
  text-align: center;
}
h1:hover ~ p {
  font-size: 30px;
  color: red;
}

External CSS

This Pen doesn't use any external CSS resources.

External JavaScript

This Pen doesn't use any external JavaScript resources.