Examine source code of Arc Theme Close Button

{
  "manifest_version": 2,
  "applications": {
    "gecko": {
      "id": "Close.trampover@gmail.com",
      "strict_min_version": "57.0a1"
    }
  },
  "name": "__MSG_extensionName__",
  "version": "1.0.3resigned1",
  "description": "__MSG_extensionDescription__",
  "icons": {
    "48": "icons/icon.svg"
  },
  "browser_action": {
    "browser_style": false,
    "default_title": "__MSG_actionTitle__",
    "default_icon": "icons/icon.svg",
    "theme_icons": [
      {
        "dark": "icons/icon.svg",
        "light": "icons/icon-light.svg",
        "size": 16
      }
    ],
    "default_area": "tabstrip"
  },
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "default_locale": "en"
}