All applications are created with a "SignIn_Control" panel which is pre-customized to perform application user sign in. This panel is used in standard Sign In pages created via the Application Builder in Iron Speed Designer. To customize the appearance of the application’s Sign In or Sign Out page, edit the page's layout page file and / or the panel's layout page file, typically found in:
...\<APP NAME>\Shared\SignIn_Control.html
These layout pages are edited just as you would any other layout page.