Add Sass CLI steps

docs/documentation/customize/concepts.html

@@ -30,6 +30,10 @@ breadcrumb:
       <strong>element/component variables</strong>: variables that are specific to a Bulma element/component
     </li>
   </ul>
+
+  <p>
+    Since these variables carry the <code>!default</code> flat, they can be assigned a <strong>new value</strong> either before or after having been imported.
+  </p>
 </div>
 
 {% include elements/anchor.html name="Strategy" %}