How to change the background of Meizu mx4pro SMS?

The SMS background can be changed by itself or by applying the theme:

One: Self-replacement requires root permission, which may cause problems. Self-replacement needs to modify the system material, and self-replacement is not recommended.

Two: At present, the themes in Meizu's own personalization generally modify the SMS background. You can choose your favorite theme to modify the SMS background and replace it (individual themes need to be paid for).