You can fully customize how the registration page looks by uploading your own HTML template file.
Use the attached html file as a starting point
Upload the file as-is to your conversation and go to the registration URL (e.g. app.voicevoice.com/yourconversation/register) to see all the basic components of a registration page and how you can customize them with your own HTML, CSS and Javascript.
Note: you can choose what elements of the template you want to include in your registration page, but for it to work properly, the following elements are required:
#registrationFormContainer #registerUrl
Also see: Registration Intermediate Pages
Setting location: Conversation Settings > Registration Page Template