polish(core): Slightly improve #342

Actually use the colors.

core/templates/core/unit_list.html

@@ -24,10 +24,18 @@
   </ul>
   <p>Next to each three letter code, there is one of the following symbols.</p>
   <ul>
-    <li>Check mark (✓) means you’ve done the unit.</li>
-    <li>Blue clock (⏲) means the unit is unlocked but not done.</li>
-    <li>Grey hourglass (⧖) means the unit is locked but on your to-do list.</li>
-    <li>No symbol (bolded black) is everything else.</li>
+    <li>
+      Check mark (<span class="text-success">✓</span>) means you've done the unit.
+    </li>
+    <li>
+      Blue clock (<span class="text-primary">⏲</span>) means the unit is unlocked but not done.
+    </li>
+    <li>
+      Grey hourglass (<span class="text-secondary">⧖</span>) means the unit is locked but on your to-do list.
+    </li>
+    <li>
+      No symbol (<b class="text-dark">bolded black</b>) is everything else.
+    </li>
   </ul>
   <p>
     This page was printed on {% now "r" %}.