Theme: Style menu header sections a little dimmer

They are hard to read if they have the same color as all other links.

templates/custom/header.tmpl

@@ -34,6 +34,11 @@
     display: none;
   }
 
+  /* Dim the "header" of sections in dropdown menus. */
+  .ui.dropdown .menu>.header:not(.ui) {
+    color: var(--color-text-light-3);
+  }
+
   /* Homepage. */
   /* By default Gitea colors links green */
   .home a {