Refactored several theme settings into custom theme

lib/core/custom_theme.dart

@@ -1,38 +1,59 @@
 import 'package:flutter/material.dart';
 
 class CustomTheme {
+  CustomTheme._(); // Private constructor to prevent instantiation
+
+  // ==================== Colors ====================
   static Color primaryColor = const Color(0xFF7505E4);
   static Color secondaryColor = const Color(0xFFAFA2FF);
   static Color backgroundColor = const Color(0xFF0B0B0B);
   static Color boxColor = const Color(0xFF101010);
   static Color onBoxColor = const Color(0xFF181818);
   static Color boxBorder = const Color(0xFF272727);
+  static const Color textColor = Colors.white;
 
+  // ==================== Border Radius ====================
+  static const double standardBorderRadius = 12.0;
+  static BorderRadius get standardBorderRadiusAll =>
+      BorderRadius.circular(standardBorderRadius);
+
+  // ==================== Padding & Margins ====================
+  static const EdgeInsets standardMargin = EdgeInsets.symmetric(
+    horizontal: 12,
+    vertical: 10,
+  );
+  static const EdgeInsets tileMargin = EdgeInsets.symmetric(
+    horizontal: 12,
+    vertical: 5,
+  );
+
+  // ==================== Decorations ====================
   static BoxDecoration standardBoxDecoration = BoxDecoration(
     color: boxColor,
     border: Border.all(color: boxBorder),
-    borderRadius: BorderRadius.circular(12),
+    borderRadius: standardBorderRadiusAll,
   );
 
   static BoxDecoration highlightedBoxDecoration = BoxDecoration(
     color: boxColor,
     border: Border.all(color: primaryColor),
-    borderRadius: BorderRadius.circular(12),
+    borderRadius: standardBorderRadiusAll,
     boxShadow: [BoxShadow(color: primaryColor.withAlpha(120), blurRadius: 12)],
   );
 
+  // ==================== App Bar Theme ====================
   static AppBarTheme appBarTheme = AppBarTheme(
     backgroundColor: backgroundColor,
-    foregroundColor: Colors.white,
+    foregroundColor: textColor,
     elevation: 0,
     scrolledUnderElevation: 0,
     centerTitle: true,
     titleTextStyle: const TextStyle(
-      color: Colors.white,
+      color: textColor,
       fontSize: 20,
       fontWeight: FontWeight.bold,
       overflow: TextOverflow.ellipsis,
     ),
-    iconTheme: const IconThemeData(color: Colors.white),
+    iconTheme: const IconThemeData(color: textColor),
   );
 }