You don't need to download it, as those borders already exist by default.
Here are some paths you can use:
- UI\Widgets\EscMenu\Orc\orc-options-menu-border.blp ( = Orc borders)
- UI\Widgets\EscMenu\Nightelf\nightelf-options-menu-border.blp ( = Nightelf borders)
- UI\Widgets\EscMenu\Human\human-options-menu-border.blp ( = Human borders)
- UI\Widgets\EscMenu\Undead\undead-options-menu-border.blp ( = Undead borders)
- UI\Widgets\Glues\GlueScreen-Button1-BackdropBorder-DisabledDown.blp ( = Random border 1)
- UI\Widgets\Glues\GlueScreen-CampaignButton-BackdropBorder-DisabledDown.blp ( = Random border 2)
Use whatever fits your map best.