set chatBackgroundColor to white instead of transparent for light theme

DcCore/DcCore/Helper/DcColors.swift

@@ -14,7 +14,7 @@ public struct DcColors {
     public static let contactCellBackgroundColor = UIColor.themeColor(light: .white, dark: .black)
     public static let defaultBackgroundColor = UIColor.themeColor(light: .white, dark: .black)
     public static let sharedChatCellBackgroundColor = UIColor.themeColor(light: white, dark: actionCellBackgroundDark)
-    public static let chatBackgroundColor = UIColor.themeColor(light: UIColor(red: 255, green: 255, blue: 255, alpha: 0), dark: .black)
+    public static let chatBackgroundColor = UIColor.themeColor(light: .white, dark: .black)
     public static let checkmarkGreen = UIColor.themeColor(light: UIColor.rgb(red: 112, green: 177, blue: 92))
     public static let defaultTextColor = UIColor.themeColor(light: .darkText, dark: .white)
     public static let grayTextColor = UIColor.themeColor(light: .darkGray, dark: .lightGray)