Enhance user experience and interface of sales and dashboard sections

Refactor UI components in NewSaleForm.tsx, SalesHistory.tsx, index.css, validation.ts, and Dashboard.tsx for improved UX.

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/c74640af-aff6-4467-98ef-6922e186fed2.jpg

client/src/pages/Dashboard.tsx

@@ -41,7 +41,7 @@ function DashboardContent() {
     <div className="min-h-screen bg-background">
       {/* Modern Header */}
       <header className="sticky top-0 z-50 border-b border-border bg-background/95 backdrop-blur supports-[backdrop-filter]:bg-background/60">
-        <div className="max-w-7xl mx-auto mobile-padding">
+        <div className="max-w-7xl mx-auto px-4 sm:px-6 lg:px-8">
           <div className="flex justify-between items-center h-16">
             <div className="flex items-center gap-4">
               <div className="relative">