style: refine dark theme colors in globals.css

- Updated background and card colors for the dark theme to enhance visual clarity and consistency.
- Adjusted comments for better understanding of color choices.

src/app/globals.css

@@ -66,9 +66,9 @@
 
 .dark {
   /* Dark theme override */
-  --background: #1e293b; /* slate-800 - encore plus clair */
+  --background: #1e293b; /* slate-800 - background principal */
   --foreground: #f1f5f9; /* slate-100 */
-  --card: #1e293b; /* slate-800 - même couleur que le background */
+  --card: #334155; /* slate-700 - plus clair que le background */
   --card-hover: #475569; /* slate-600 */
   --card-column: #0f172a; /* slate-900 - plus foncé que les cartes */
   --border: #64748b; /* slate-500 - encore plus clair */