Examine source code of Shortcut Sensei

{
  "name": "Shortcut Sensei",
  "version": "22.4.1",
  "description": "Learn keyboard shortcuts for popular webapps!",
  "homepage_url": "https://github.com/janmechtel/shortcutsensei",
  "manifest_version": 2,
  "minimum_chrome_version": "74",
  "applications": {
    "gecko": {
      "id": "rocketkeys-beta@github.com",
      "strict_min_version": "67.0"
    }
  },
  "icons": {
    "128": "/icon128x128.png"
  },
  "permissions": [
    "storage"
  ],
  "options_ui": {
    "chrome_style": true,
    "page": "/options/options.html"
  },
  "background": {
    "persistent": false,
    "scripts": [
      "/background.js"
    ]
  },
  "browser_action": {
    "default_icon": "/icon_browser_action128x128.png",
    "default_title": "Shortcut Sensei",
    "default_popup": "/popup/popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://mail.google.com/*"
      ],
      "js": [
        "/apps/gmail/gmail.js"
      ],
      "css": [
        "/alertify.css"
      ]
    }
  ],
  "web_accessible_resources": [
    "/onboarding/onboarding.html",
    "/onboarding/onboarding.js",
    "/onboarding/typeit_index.umd.js"
  ]
}