Updates dashboard UI and improves styling

Improves the dashboard's appearance and user experience by updating styles and layouts.

Changes include:
- Updates to color schemes and spacing for better readability and visual appeal.
- Implements a responsive layout for the header to adapt to different screen sizes.
- Refactors button styles for consistency and clarity.
- Adds a gradient background to the main dashboard page.
- Updates the NextAuth URL in the development environment.

postcss.config.mjs

@@ -0,0 +1,6 @@
+const config = {
+    plugins: {
+        "@tailwindcss/postcss": {},
+    },
+};
+export default config;