Resolve "Fix display/layout/style"

Closes #14 (closed)

lib/cpu_level_page.dart

@@ -26,7 +26,7 @@ class CpuLevelPage extends StatelessWidget {
                 '☺️ FACILE',
                 style: Theme.of(context)
                     .textTheme
-                    .display1
+                    .headline4
                     .copyWith(color: Colors.black),
               ),
               onPressed: () {
@@ -48,7 +48,7 @@ class CpuLevelPage extends StatelessWidget {
                 '🤔 DIFFICILE',
                 style: Theme.of(context)
                     .textTheme
-                    .display1
+                    .headline4
                     .copyWith(color: Colors.white),
               ),
               onPressed: () {
@@ -70,7 +70,7 @@ class CpuLevelPage extends StatelessWidget {
                 '🤯 TRES DIFFICILE',
                 style: Theme.of(context)
                     .textTheme
-                    .display1
+                    .headline4
                     .copyWith(color: Colors.white),
               ),
               onPressed: () {