<main class="main container">
  <section class="section relative">
    <h2><code>position: relative;</code></h2>
    <div class="box"></div>
    <p>The above box has <strong><code>position: relative;</code></strong></p>
  </section>
  <p>Note how the <code>div.relative</code> element appears in the normal flow of document.</p>
  <p>Then the element is placed <em>relative to itself</em> depending on the values of <code>top, right, left, bottom</code>.</p>
  <p>In the above example, the box is placed <br />
    <strong style="display: inline-block; margin-top: 0.1rem; padding: 0.5rem 1rem; background-color:yellowgreen;">
      <code>
        div.relative {
        position: relative;
        left: 50%;
        top: 5em;
        }
      </code>
    </strong>
  </p>
</main>

* {
  box-sizing: border-box;
  padding: 0;
  margin: 0;
}

body {
  font-family: Arial, Helvetica, sans-serif;
  height: 100%;
}

.container {
  margin: auto;
  max-width: 900px;
  padding: 1rem;
}

.main > p {
  margin: 1rem 0 0 0;
  text-align: center;
}

.section {
  padding: 1rem;
  margin: 2rem auto;
  max-width: 400px;
  background-color: lightskyblue;
  /* text-align: center; */
  color: white;
  max-width: 100%;
}

.section h2 {
  font-size: 1.3rem;
  background-color: darkgreen;
  padding: 1rem;
}

.section p {
  font-size: 1.1rem;
  background-color: darkgreen;
  padding: 1rem;
}

.section .box {
  background-color: navy;
  width: 200px;
  height: 200px;
  margin: 2rem 0;
}

section.relative .box {
  position: relative;
  left: 50%;
  top: 5em;
}