Refactor styles and restructure CSS files

- Removed App.css and migrated styles to individual component and page-specific CSS files.
- Created base styles in base.css for layout utilities and common elements.
- Added component-specific styles in cards.css, header.css, and other relevant files.
- Updated imports in App.tsx and other components to reflect new CSS structure.
- Enhanced responsiveness and visual consistency across various components and pages.

src/components/contentCard.tsx

@@ -1,3 +1,5 @@
+import "../styles/components/cards.css";
+
 interface ContentCardProps {
   children: React.ReactNode;
   className?: string;