defined by the <code>@property</code> rule, for example <code>--ff-sans</code>, which sets the sans serif
font face.</li>
<li><em>Rules</em> or <em>Classes</em> are CSS classes you’d use in your HTML, for example <code>fw-4</code> for a font weight of 400.</li>
</ul>
<p>When <code>src/js/build.js</code> runs, it processes all of this information.  It is based on PostCSS and does the following:</p>
<ol>
<li><code>@import</code> properties are applied to create a single <code>.css</code> file</li>
<li>For e