added oled theme and theme presets

BalanceFlutter/lib/ui/app_theme.dart

@@ -0,0 +1,65 @@
+import 'package:flutter/material.dart';
+import '../domain/appearance.dart';
+
+class BalanceThemes {
+  static ThemeData build(Brightness brightness, ColorPreset preset) {
+    final oled = brightness == Brightness.dark && preset == ColorPreset.oled;
+    var scheme = ColorScheme.fromSeed(
+      seedColor: Color(preset.seedArgb),
+      brightness: brightness,
+    );
+    if (oled) {
+      scheme = scheme.copyWith(
+        surface: Colors.black,
+        surfaceDim: Colors.black,
+        surfaceBright: Colors.black,
+        surfaceContainerLowest: Colors.black,
+        surfaceContainerLow: Colors.black,
+        surfaceContainer: Colors.black,
+        surfaceContainerHigh: Colors.black,
+        surfaceContainerHighest: Colors.black,
+        surfaceTint: Colors.transparent,
+        primaryContainer: Colors.black,
+        onPrimaryContainer: scheme.onSurface,
+        secondaryContainer: const Color(0xff171b19),
+        outlineVariant: const Color(0xff303633),
+      );
+    }
+    return ThemeData(
+      useMaterial3: true,
+      fontFamily: 'BalanceRoboto',
+      colorScheme: scheme,
+      scaffoldBackgroundColor: scheme.surface,
+      canvasColor: scheme.surface,
+      applyElevationOverlayColor: !oled,
+      inputDecorationTheme: const InputDecorationTheme(
+        border: OutlineInputBorder(),
+      ),
+      cardTheme: CardThemeData(
+        surfaceTintColor: oled ? Colors.transparent : null,
+        shape: RoundedRectangleBorder(
+          borderRadius: BorderRadius.circular(24),
+          side: oled
+              ? BorderSide(color: scheme.outlineVariant)
+              : BorderSide.none,
+        ),
+      ),
+      appBarTheme: AppBarTheme(
+        backgroundColor: scheme.surface,
+        surfaceTintColor: oled ? Colors.transparent : null,
+        centerTitle: false,
+      ),
+      navigationBarTheme: NavigationBarThemeData(
+        backgroundColor: oled ? Colors.black : null,
+        surfaceTintColor: oled ? Colors.transparent : null,
+      ),
+      navigationRailTheme: NavigationRailThemeData(
+        backgroundColor: oled ? Colors.black : null,
+      ),
+      dialogTheme: DialogThemeData(
+        backgroundColor: oled ? Colors.black : null,
+        surfaceTintColor: oled ? Colors.transparent : null,
+      ),
+    );
+  }
+}