<p><a href="#">This</a> is a text link on a light background.</p>
<p><a class="usa-color-text-visited" href="#">This</a> is a visited link.</p>
<p>This is a link that goes to an <a class="usa-external_link" href="http://media.giphy.com/media/8sgNa77Dvj7tC/giphy.gif">external website</a>.</p>
<div class="usa-background-dark">
<p><a href="#">This</a> is a text link on a dark background.</p>
</div>