Update theme handling and add theme selection dropdown in Navbar.svelte

src/routes/+page.server.ts

@@ -30,7 +30,8 @@ export const actions: Actions = {
   },
   setTheme: async ( { url, cookies }) => {
     const theme = url.searchParams.get("theme");
-    if (theme) {
+    // change the theme only if it is one of the allowed themes
+    if (theme && ["light", "dark", "night", "retro", "forest"].includes(theme)) {
       cookies.set("colortheme", theme, {
         path: "/",
         maxAge: 60 * 60 * 24 * 365,

src/routes/login/+page.svelte

@@ -55,7 +55,7 @@
 </div>
 
 {#if errors.message}
-  <div class="text-center text-red-500 mt-4">
+  <div class="text-center text-error mt-4">
     {errors.message}
   </div>
 {/if}