There are three data entry type screens in ROKU. The keyboard screen, the search screen, and the pin entry screen. Anything else you would need to create yourself.
The keyboard screen has an overhang image as well as support for breadcrumbs, so you could change the colors and text at the top of the screen with an image for the overhang.
You can also change the search text and preload a 'search term'. So you have more control over entering a PIN code and your PIN can be alphanumeric using the search/keyboard screen.
The search screen also allows for an overhang graphic.
I'm sure KBenson and TheEndless would urge you to check into roImageCanvas, as that would allow you to accomplish any kind of graphical interface with nearly full control over how it works. Ideally that's what you'd want for a finalized product, but as a short term fix you can use one of the three built-in screen types.