Examine source code of button grid darkness

{
  "theme": {
    "images": {
      "theme_frame": "buton_grid_darkness1.jpg"
    },
    "colors": {
      "frame": "#424141",
      "tab_background_text": "#4f4952"
    }
  },
  "version": "2.0",
  "name": "button grid darkness",
  "manifest_version": 2,
  "description": "dark dimpled surface with lighting"
}