Refactor variable naming

forui/lib/src/box/box.dart

@@ -16,7 +16,7 @@ class FBox extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
-    final style = this.style ?? FTheme.of(context).widgetData.fBoxStyle;
+    final style = this.style ?? FTheme.of(context).widgetData.boxStyle;
 
     return ColoredBox(
       color: style.color,

forui/lib/src/theme/widget_data.dart

@@ -1,16 +1,17 @@
 import 'package:forui/src/box/box_style.dart';
 
+/// A class that holds the widget data.
 class FWidgetData {
   /// The box style.
-  final FBoxStyle fBoxStyle;
+  final FBoxStyle boxStyle;
 
   /// Creates a [WidgetData].
-  FWidgetData({required this.fBoxStyle});
+  FWidgetData({required this.boxStyle});
 
   /// Creates a copy of this [FWidgetData] with the given properties replaced.
   FWidgetData copyWith({
-    FBoxStyle? fBoxStyle,
+    FBoxStyle? boxStyle,
   }) => FWidgetData(
-      fBoxStyle: fBoxStyle ?? this.fBoxStyle,
+      boxStyle: boxStyle ?? this.boxStyle,
     );
 }