Sections

<html lang="en">
  <head>
    <title>Document title</title>
  </head>
  <body>
    <p>
      The <code>&lt;body&gt;</code> HTML element represents the content of an
      HTML document. There can be only one <code>&lt;body&gt;</code> element in
      a document.
    </p>
  </body>
</html>

<article class="forecast">
  <h1>Weather forecast for Seattle</h1>
  <article class="day-forecast">
    <h2>03 March 2018</h2>
    <p>Rain.</p>
  </article>
  <article class="day-forecast">
    <h2>04 March 2018</h2>
    <p>Periods of rain.</p>
  </article>
  <article class="day-forecast">
    <h2>05 March 2018</h2>
    <p>Heavy rain.</p>
  </article>
</article>

.forecast {
  margin: 0;
  padding: 0.3rem;
  background-color: #eeeeee;
}

.forecast > h1,
.day-forecast {
  margin: 0.5rem;
  padding: 0.3rem;
  font-size: 1.2rem;
}

.day-forecast {
  background: right/contain content-box border-box no-repeat
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}

.day-forecast > h2,
.day-forecast > p {
  margin: 0.2rem;
  font-size: 1rem;
}

<h1>Choosing an Apple</h1>
<section>
  <h2>Introduction</h2>
  <p>
    This document provides a guide to help with the important task of choosing
    the correct Apple.
  </p>
</section>

<section>
  <h2>Criteria</h2>
  <p>
    There are many different criteria to be considered when choosing an Apple —
    size, color, firmness, sweetness, tartness...
  </p>
</section>

h1,
h2 {
  margin: 0;
}

<nav class="crumbs">
  <ol>
    <li class="crumb"><a href="#">Bikes</a></li>
    <li class="crumb"><a href="#">BMX</a></li>
    <li class="crumb">Jump Bike 3000</li>
  </ol>
</nav>

<h1>Jump Bike 3000</h1>
<p>
  This BMX bike is a solid step into the pro world. It looks as legit as it
  rides and is built to polish your skills.
</p>

nav {
  border-bottom: 1px solid black;
}

.crumbs ol {
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.crumb {
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}

.crumb a::after {
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  content: ">";
  font-size: 80%;
  font-weight: bold;
  padding: 0 3px;
}

<p>
  Salamanders are a group of amphibians with a lizard-like appearance, including
  short legs and a tail in both larval and adult forms.
</p>

<aside>
  <p>The Rough-skinned Newt defends itself with a deadly neurotoxin.</p>
</aside>

<p>
  Several species of salamander inhabit the temperate rainforest of the Pacific
  Northwest, including the Ensatina, the Northwestern Salamander and the
  Rough-skinned Newt. Most salamanders are nocturnal, and hunt for insects,
  worms and other small creatures.
</p>

aside {
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  margin-left: 0.5rem;
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  box-shadow: inset 5px 0 5px -5px #29627e;
  font-style: italic;
  color: #29627e;
}

aside > p {
  margin: 0.5rem;
}

<h1>Beetles</h1>
<h2>External morphology</h2>
<h3>Head</h3>
<h4>Mouthparts</h4>
<h3>Thorax</h3>
<h4>Prothorax</h4>
<h4>Pterothorax</h4>

h1,
h2,
h3,
h4 {
  margin: 0.1rem 0;
}

h1 {
  font-size: 2rem;
}

h2 {
  font-size: 1.5rem;
  padding-left: 20px;
}

h3 {
  font-size: 1.2rem;
  padding-left: 40px;
}

h4 {
  font-size: 1rem;
  font-style: italic;
  padding-left: 60px;
}

<hgroup>
  <h1>Frankenstein</h1>
  <p>Or: The Modern Prometheus</p>
</hgroup>
<p>
  Victor Frankenstein, a Swiss scientist, has a great ambition: to create
  intelligent life. But when his creature first stirs, he realizes he has made a
  monster. A monster which, abandoned by his master and shunned by everyone who
  sees it, follows Dr Frankenstein to the very ends of the earth.
</p>

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}

hgroup h1 {
  margin-bottom: 0;
}

hgroup p {
  margin: 0;
  font-weight: bold;
}

<header>
  <a class="logo" href="#">Cute Puppies Express!</a>
</header>

<article>
  <header>
    <h1>Beagles</h1>
    <time>08.12.2014</time>
  </header>
  <p>
    I love beagles <em>so</em> much! Like, really, a lot. They're adorable and
    their ears are so, so snugly soft!
  </p>
</article>

.logo {
  background: left / cover
    url("https://developer.mozilla.org/shared-assets/images/examples/puppy-header.jpg");
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  height: 120px;
  align-items: center;
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  font:
    bold calc(1em + 2 * (100vw - 120px) / 100) "Dancing Script",
    fantasy;
  color: #ff0083;
  text-shadow: black 2px 2px 0.2rem;
}

header > h1 {
  margin-bottom: 0;
}

header > time {
  font: italic 0.7rem sans-serif;
}

<article>
  <h1>How to be a wizard</h1>
  <ol>
    <li>Grow a long, majestic beard.</li>
    <li>Wear a tall, pointed hat.</li>
    <li>Have I mentioned the beard?</li>
  </ol>
  <footer>
    <p>© 2018 Gandalf</p>
  </footer>
</article>

article {
  min-height: 100%;
  display: grid;
  grid-template-rows: auto 1fr auto;
}

footer {
  display: flex;
  justify-content: center;
  padding: 5px;
  background-color: #45a1ff;
  color: white;
}

<p>Contact the author of this page:</p>

<address>
  <a href="mailto:jim@example.com">jim@example.com</a><br />
  <a href="tel:+14155550132">+1 (415) 555‑0132</a>
</address>

a[href^="mailto"]::before {
  content: "📧 ";
}

a[href^="tel"]::before {
  content: "📞 ";
}