Section - CSS does not work

Question

I’m having a problem with the Section of my code. It is all without formatting, I cleaned the browser cache to see if it worked and still not getting CSS.

.newsletter {
  width: 100%;
  float: left;
  text-align: center;
  padding: 3% 4%;
  background-color: #130400;
}

.newsletter h2 {
  font-size: 1.5em;
  color: #fff;
  font-weight: 700;
}

.newsletter h3 {
  color: #fff;
}

.newsletter form {
  margin-top: 2%;
}

<section class="newsletter">
  <h2> Inscreva-se agora! </h2>
  <h3> Receba novidades, dicas e muito mais. </h3>
  <form>
    <input type="email" name="email" placeholder="digite seu email">
    <button> Cadastrar </button>
  </form>
</section>