feat(ui_kit): allow to cascade styles in ThemeHelper

packages/wyatt_ui_kit/example/lib/bars/bars.dart

@@ -77,7 +77,7 @@ class Bars extends DemoPage {
               ),
             ],
             navigationItems: [
-              'ACCEUIL'.wrap(),
+              'ACCEUIL'.wrap(style: const TextStyle(color: Colors.red)),
               'VOTRE PROGRAMME'.wrap(),
               'LE STUDIO'.wrap(),
               'SAVOIR FAIRE'.wrap()

packages/wyatt_ui_kit/example/lib/theme/top_bar_theme.dart

@@ -25,6 +25,7 @@ class TopAppBarTheme extends TopBarThemeExtension {
         subTitleStyle: GoogleFonts.montserrat(
           fontWeight: FontWeight.w400,
           color: const Color.fromRGBO(36, 38, 42, 1),
+          fontStyle: FontStyle.italic,
           fontSize: 18,
         ),
         iconTheme: const IconThemeData(color: Color.fromRGBO(36, 38, 42, 1)),
@@ -43,6 +44,7 @@ class TopAppBarTheme extends TopBarThemeExtension {
         ),
         subTitleStyle: GoogleFonts.montserrat(
           fontWeight: FontWeight.w400,
+          fontStyle: FontStyle.italic,
           fontSize: 18,
         ),
         iconTheme: const IconThemeData(color: Colors.white),