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.

app/globals.css

@@ -7,3 +7,5 @@ input,
 button {
   font-family: inherit;
 }
+
+@import "tailwindcss";