Examine source code of Dull Skull

{
  "name": "Dull Skull",
  "manifest_version": 2,
  "version": "3.0",
  "theme": {
    "images": {
      "theme_frame": "skull-2.png"
    },
    "colors": {
      "frame": "rgba(229, 230, 232, 1)",
      "tab_background_text": "rgba(204, 204, 204, 1)",
      "toolbar": "rgba(0, 0, 0, 0.46)",
      "bookmark_text": "rgba(196, 196, 196, 1)",
      "toolbar_field": "rgba(3, 3, 3, 0.52)",
      "toolbar_field_text": "rgba(189, 189, 189, 1)",
      "tab_line": "rgba(158, 130, 47, 1)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{7d672add-0c9b-4308-8a15-f2277e1d2803}"
    }
  }
}