This page consists of screenshots from the Subscription Form Design – Success Message Screen in Coming Soon Booster WordPress Plugin.
This gives an idea about how to configure Success Message Settings. You can easily customize the success message which has to be displayed to the users, when they successfully subscribes to your website.
Using Success Message Settings, you can provide content for Success Message which you would like to display when user successfully submits the subscription form. You can also customize the Color, Font, Background, Margin and Padding for the success message.