Explain Flutter themes and styling.

Flutter themes and styling:\n\n**ThemeData:**\n\nMaterialApp(\n theme: ThemeData(\n primarySwatch: Colors.blue,\n accentColor: Colors.orange,\n fontFamily: 'Roboto',\n textTheme: TextTheme(\n headline1: TextStyle(fontSize: 24, fontWeight: FontWeight.bold)\n )\n )\n)\n\n\n**Custom themes:**\n\nThemeData.light().copyWith(\n primaryColor: Colors.purple,\n buttonTheme: ButtonThemeData(\n buttonColor: Colors.purple,\n textTheme: ButtonTextTheme.primary\n )\n)\n\n\n**Using themes:**\n\n// Access theme\nfinal theme = Theme.of(context);\nText(\n 'Styled text',\n style: theme.textTheme.headline1\n)\n\n\n**Dark theme:**\n\nMaterialApp(\n theme: ThemeData.light(),\n darkTheme: ThemeData.dark(),\n themeMode: ThemeMode.system\n)\n\n\n**Custom styling:**\n• TextStyle for text appearance\n• BoxDecoration for containers\n• Material Design components