<section class="links">
  <p><a href="https://www.css-tricks.com" class="csstricks">This link goes to CSS-Tricks. After it's been visited, it will turn orange.</a></p>
  <p><a href="https://www.codepen.io" class="codepen">This link goes to CodePen. After it's been visited, its border will turn black.</a></p>
  <p><a href="https://www.google.com" class="google">This link goes to Google. After it's been visited, it will turn white and the background will turn orange. </a></p>
</section>

a.csstricks {
  color: green;
}

a.csstricks:visited {
  color: #E18728;
}

a.codepen {
  border: 2px solid blue;
}

a.codepen:visited {
  border: 2px solid black;
}

a.google {
  background-color: yellow;
  color: black;
}

a.google:visited {
  background-color: #E18728;
  color: white;
}
/* Pen styling, unrelated to :visited */

.links {
  max-width: 70vw;
  margin: 0 auto;
  font-size: 1.5em;
  font-family: 'Source Sans Pro', sans-serif;
}