<div class="hero-section">
  <h1>it's hero title</h1>
  <p>it's hero description</p>
</div>

html {
  font-size: 62.5%;
}

body {
  font-size: 1.6rem;
  margin: 0;
}

.hero-section {
  font-size: 1rem;
}

h1 {
  background: red;
  font-size: 4em;
  margin: 1em 0;
}

p {
  background: lightblue;
  font-size: 2em;
  margin: 1em 0;
}

@media (max-width: 500px) {
  .hero-section {
    font-size: .5em;
  }
}