Use systemGray and gradient

(cherry picked from commit 3a09cb4343802b65508a3fb1ed7e07135b909889)

FreeAPS/Sources/Modules/Bolus/View/BolusRootView.swift

@@ -222,8 +222,7 @@ extension Bolus {
                 }.padding(.bottom, 10)
             }
             .background(
-                RoundedRectangle(cornerRadius: 8, style: .continuous)
-                    .fill(Color(colorScheme == .dark ? UIColor.systemGray4 : UIColor.systemGray4))
+                RoundedRectangle(cornerRadius: 8, style: .continuous).fill(Color(.systemGray).gradient)
             )
         }
     }