Missing Text in Customizer

When using customizer (which appears to be the only way to use this plugin) there is no text displayed for messages that appear under the logo and above the form. These are messages such as “Register For This Site” and “Registration complete. Please check your email.” But because they are not displayed in customizer there seems to be no way to set them. When I choose a dark background these messages disappear.

Is there any way to access these messages to set them? Or maybe I could style them somehow? Thanks!