Borders [genesis_plus_gx_overscan] (core option)

Enable this to display the overscan regions at the top/bottom and/or left/right of the screen. These would normally be hidden by the bezel around the edge of a standard-definition television.

• Off [disabled] - Disables displaying the game's overscan regions.
• Top/Bottom [top/bottom] - Enables displaying the game's Top and Bottom overscan regions.
• Left/Right [left/right] - Enables displaying the game's Left and Right overscan regions.
• Full [full] - Enables displaying the game's Top/Bottom and Left/Right overscan regions.

Game is: Sparkster

DISCLAIMER: Libretro can do whatever with these videos. Or maybe someone can make even better videos. These video demonstrations of core options and such were made just so users would have at least have something to use as an animated visual reference.