Change the Confirmation email template
You can create and style a new template on the Emails > Templates Screen. The system starter template is pre setup to be ready to use for a confirmation email. All you need to do is either edit its styles or clone it to a new template and style away.
Once you have that setup you can then go to Settings > Confirmation. If you scroll to the bottom you will see an option to pick your template. Now that you have updated the settings the next confirmation email that gets sent should use your new template.