fix: monospace class use --ft-mono (#61)

Author: feored

styles/@utilities/classes.html

@@ -55,7 +55,7 @@ <h3 id="utilities-classes-list">
           <code data-hl="css">.justified</code> sets <code data-hl="css">text-align: justify;</code>
         </li>
         <li>
-          <code data-hl="css">.monospace</code> sets <code data-hl="css">font-family: var(--mono);</code>
+          <code data-hl="css">.monospace</code> sets <code data-hl="css">font-family: var(--ft-mono);</code>
         </li>
       </ul>
     </li>

styles/@utilities/mod.css

@@ -208,7 +208,7 @@
 }
 
 .monospace {
-  font-family: var(--mono);
+  font-family: var(--ft-mono);
 }
 
 /* Font size */