Fix push subscription settings GroupBox background in dark mode

Closes #470

Tusker/Screens/Preferences/Notifications/PushSubscriptionView.swift

@@ -77,6 +77,7 @@ private struct PushSubscriptionSettingsView: View {
                 // status notifications not supported until we can enable/disable them in the app
             }
         }
+        .groupBoxStyle(AppBackgroundGroupBoxStyle())
     }
     
     private var allSupportedAlertTypes: PushSubscription.Alerts {
@@ -125,6 +126,19 @@ private extension PushSubscription.Policy {
     }
 }
 
+private struct AppBackgroundGroupBoxStyle: GroupBoxStyle {
+    func makeBody(configuration: Configuration) -> some View {
+        VStack(alignment: .leading, spacing: 16) {
+            configuration.label
+                .font(.headline)
+            
+            configuration.content
+        }
+        .padding()
+        .background(Color.appGroupedBackground, in: RoundedRectangle(cornerRadius: 8))
+    }
+}
+
 //#Preview {
 //    PushSubscriptionView()
 //}