minecraft-assets/assets/minecraft/models/block/quartz_stairs_outer.json

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