Examine source code of Dark Themem

{
  "manifest_version": 2,
  "version": "0.1.1",
  "name": "Dark Theme for Facebook™",
  "description": "__MSG_app_description__",
  "default_locale": "en",
  "permissions": [
    "storage",
    "alarms",
    "idle"
  ],
  "background": {
    "persistent": false,
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.facebook.com/*",
        "*://*.messenger.com/*"
      ],
      "js": [
        "data/inject.js"
      ],
      "css": [
        "data/styles/common.css"
      ],
      "run_at": "document_start",
      "all_frames": true
    }
  ],
  "icons": {
    "16": "data/icons/16.png",
    "32": "data/icons/32.png",
    "48": "data/icons/48.png",
    "64": "data/icons/64.png",
    "128": "data/icons/128.png",
    "256": "data/icons/256.png",
    "512": "data/icons/512.png"
  },
  "homepage_url": "https://add0n.com/dark-theme.html?from=facebook",
  "options_ui": {
    "page": "data/options/index.html",
    "chrome_style": true
  },
  "browser_action": {},
  "browser_specific_settings": {
    "gecko": {
      "id": "{538ad176-7a83-421c-a939-a47399e6b304}"
    }
  }
}