adding missing const

frontend/lib/constants.dart

@@ -26,13 +26,13 @@ ThemeData APP_THEME = ThemeData(
   cardColor: Colors.white,
   useMaterial3: true,
 
-  colorScheme: ColorScheme.light(
+  colorScheme: const ColorScheme.light(
     primary: PRIMARY_COLOR,
     secondary: GRADIENT_END,
     surface: Colors.white,
     error: Colors.red,
     onPrimary: Colors.white,
-    onSecondary: const Color.fromARGB(255, 30, 22, 22),
+    onSecondary: Color.fromARGB(255, 30, 22, 22),
     onSurface: Colors.black,
     onError: Colors.white,
     brightness: Brightness.light,
@@ -64,12 +64,6 @@ ThemeData APP_THEME = ThemeData(
   ),
 
 
-  cardTheme: const CardTheme(
-    shadowColor: Colors.grey,
-    elevation: 2,
-    margin: EdgeInsets.all(10),
-  ),
-
   sliderTheme: const SliderThemeData(
     trackHeight: 15,
     inactiveTrackColor: Colors.grey,
@@ -83,4 +77,4 @@ const Gradient APP_GRADIENT = LinearGradient(
   begin: Alignment.topLeft,
   end: Alignment.bottomRight,
   colors: [GRADIENT_START, GRADIENT_END],
-);
+);