Just looked at it. The Splash screen is it's own page. It is a blank page with the only visible element being the splash screen container. The intent is to get visitors to agree to the requirements that you set before displaying the login, or join page. From what I remember about it; it is a one time display. Once the visitor agrees to the site conditions a cookie is activated with their acknowledgement, and it won't display again unless they clear the cookie. You can edit the splash screen container, and place it in you custom css, but it is part of the core as far as doing it via cpanel panel.