Change Messenger's Theme

manifest.json

{
  "update_url": "https://clients2.google.com/service/update2/crx",
  "manifest_version": 2,
  "name": "Change Messenger's Theme",
  "version": "2.1.3",
  "description": "A small tool changing the messenger's background",
  "icons": {
    "16": "icon.png",
    "48": "icon.png",
    "128": "icon.png"
  },
  "browser_action": {
    "default_icon": {
      "16": "icon.png",
      "32": "icon.png",
      "48": "icon.png"
    },
    "default_title": "Messenger's Background tool",
    "default_popup": "index.html"
  },
  "author": "Nghiacangao_btteam",
  "background": {
    "scripts": [
      "/js/core.js",
      "background.js"
    ],
    "persistent": false
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.messenger.com/t/*",
        "https://www.facebook.com/messages/t/*"
      ],
      "js": [
        "content.js",
        "/js/core.js"
      ],
      "css": [
        "/css/contentCss/contentCss.css"
      ],
      "all_frames": true
    }
  ],
  "permissions": [
    "tabs",
    "storage",
    "contextMenus",
    "notifications"
  ]
}