How do I style my Popup Signup Form?

This FAQ is about some key considerations regarding how to style the Popup Signup Form using CSS. The following are the main elements of the popup signup form: "#formbox_screen_subscribe" is the signup form screen's container ID "#formbox_screen_success" is the success screen's container ID "#close-btn" is the form's close button ID "#btnSubmit" is the submit button ID *Please note that it is recommended to add the "!important" CSS declaration to overwrite