fix: mobile dropdown bg uses --color-dropdown-bg for dark theme

src/styles/main.css

@@ -287,7 +287,7 @@ nav details.nav-group details a.nav-link {
     max-height: calc(100vh - 3.5rem);
     overflow-y: auto;
     z-index: 100;
-    background-color: var(--color-navy);
+    background-color: var(--color-dropdown-bg);
     padding: 1rem;
     border-radius: 0;
     box-shadow: none;