<h6><span>&lt;h6&gt;</span>Heading 6<span>&lt;/h6&gt;</span></h6>
<h5><span>&lt;h5&gt;</span>Heading 5<span>&lt;/h5&gt;</span></h5>
<h4><span>&lt;h4&gt;</span>Heading 4<span>&lt;/h4&gt;</span></h4>
<h3><span>&lt;h3&gt;</span>Heading 3<span>&lt;/h3&gt;</span></h3>
<h2><span>&lt;h2&gt;</span>Heading 2<span>&lt;/h2&gt;</span></h2>
<h1><span>&lt;h1&gt;</span>Heading 1<span>&lt;/h1&gt;</span></h1>
<h2><span>&lt;h2&gt;</span>Heading 2<span>&lt;/h2&gt;</span></h2>
<h3><span>&lt;h3&gt;</span>Heading 3<span>&lt;/h3&gt;</span></h3>
<h4><span>&lt;h4&gt;</span>Heading 4<span>&lt;/h4&gt;</span></h4>
<h5><span>&lt;h5&gt;</span>Heading 5<span>&lt;/h5&gt;</span></h5>
<h6><span>&lt;h6&gt;</span>Heading 6<span>&lt;/h6&gt;</span></h6>

index.html

body {
  background-color: black;
  color: white;
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
  height: 100vh;
  margin: 0;
  padding: 0;
  text-align: center;
}
h1, h2, h3, h4, h5, h6 {
  margin: 0.5em;
  font-weight: normal;
}
span {
  font-family: monospace;
}

index.css