Examine source code of DarkTheme VK

{
  "manifest_version": 2,
  "name": "DarkTheme",
  "version": "0.6",
  "description": "DarkTheme for VK.",
  "icons": {
    "48": "icons/border-48.png"
  },
  "browser_action": {
    "browser_style": true,
    "default_icon": {
      "48": "icons/border-48.png"
    },
    "default_title": "DarkTheme"
  },
  "applications": {
    "gecko": {
      "id": "kot06opmot@ms.com"
    }
  },
  "content_scripts": [
    {
      "matches": [
        "*://vk.com/*"
      ],
      "css": [
        "css/dark.css"
      ]
    }
  ]
}