Modernize the user interface by reducing rounded corners across the platform

Updates border-radius values in index.css for a more angular design and updates replit.md to reflect changes.

Replit-Commit-Author: Agent
Replit-Commit-Session-Id: dec54137-d5a2-4406-8ad4-5f2f9fb110bf
Replit-Commit-Screenshot-Url: https://storage.googleapis.com/screenshot-production-us-central1/0715008c-7244-40f4-befc-26c014852236/b11a2e40-a490-44b4-89fd-fb617b0622ec.jpg

replit.md

@@ -243,6 +243,9 @@ Preferred communication style: Simple, everyday language.
 - ✅ Added date and time display in sales history with automatic timestamp from database
 - ✅ Harmonized color scheme in new sale form with softer, complementary colors
 - ✅ Updated section backgrounds to work cohesively with green save button
+- ✅ Uniformized export buttons with consistent styling
+- ✅ Applied angular design with reduced border-radius throughout entire application
+- ✅ Modern, crisp appearance with 4px border-radius for cards, inputs, and buttons
 
 ### Docker Configuration & Cleanup (January 9, 2025)
 - ✅ Complete Docker setup optimized for external PostgreSQL database