source-code/desktopRuntime/resources/assets/minecraft/models/block/cobblestone_stairs_outer.json

{
  "parent": "minecraft:block/outer_stairs",
  "textures": {
    "bottom": "minecraft:block/cobblestone",
    "side": "minecraft:block/cobblestone",
    "top": "minecraft:block/cobblestone"
  }
}