This is a mod that allows you to modify basic alerts, such as when a player joins, leaves or dies with a json setting. In addition, it allows infinite customization in messages by adding a message with a style and color depending on your taste, in addition to being able to modify the json manually using /cva config reload to make the corresponding changes in the mod, the format. You can find it on the official Formatting page of the minecraft wiki https://minecraft.fandom.com/wiki/Formatting_codes