<div class="section-wrapper">
  <section class="section">
    <div class="section__item section__item--start">
      <h2>Sign up now</h2>
      <p>We're glad that you want to know more about our business.
      </p>
    </div>

    <div class="section__item section__item--end">
      <ul>
        <li>100% free account.</li>
        <li>No ads.</li>
        <li>Cancel at anytime, no questions asked.</li>
      </ul>
    </div>
  </section>
</div>

.section-wrapper {
  container-type: inline-size;
  resize: horizontal;
  overflow: hidden;
  max-width: 800px;
  margin: 1rem auto;
}

.section {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  padding: 1rem;

  &:before {
    content: "";
    align-self: stretch;
    border: 1px solid lightgrey;
  }
}

@container (inline-size >= 600px) {
  .section {
    flex-direction: row;
    align-items: center;
  }
}

.section__item {
  flex: 1;
  min-width: 0;
  overflow-wrap: break-word;
}

.section__item--start {
  order: -1;
}

p {
  color: #222;
}

*,
*:before,
*:after {
  box-sizing: border-box;
}