Examine source code of Calm Colors

{
  "manifest_version": 2,
  "name": "Calm Colors",
  "short_name": "Calm Colors",
  "description": "Tone down web page colors for comfort and readability..",
  "version": "1.0.6resigned1",
  "homepage_url": "https://github.com/marekjedlinski/webext-calm-colors",
  "author": "Marek Jedliński",
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "content_scripts": [
    {
      "matches": [
        "<all_urls>"
      ],
      "js": [
        "calmcolors.js"
      ]
    }
  ],
  "icons": {
    "48": "icons/calmcolors_48.png"
  },
  "permissions": [
    "tabs",
    "storage",
    "contextMenus"
  ],
  "web_accessible_resources": [
    "css/*.css"
  ],
  "applications": {
    "gecko": {
      "id": "webext-calmcolors@tranglos.com",
      "strict_min_version": "57.0"
    }
  }
}