Examine source code of About:black

{
  "manifest_version": 2,
  "version": "1.1.1",
  "name": "About:black",
  "author": "Carlos Jeurissen",
  "homepage_url": "https://apps.jeurissen.co/about-black",
  "developer": {
    "name": "Carlos Jeurissen",
    "url": "https://apps.jeurissen.co/"
  },
  "content_security_policy": "default-src 'none'; child-src 'none'; manifest-src 'none'; media-src 'none'; object-src 'none'; prefetch-src 'none'; worker-src 'none'; connect-src 'none'; frame-src 'none'; font-src 'none'; img-src 'none'; script-src 'self'; script-src-attr 'none'; script-src-elem 'self'; style-src 'none'; style-src-attr 'none'; style-src-elem 'none'; frame-ancestors 'none'; base-uri 'none'; form-action 'none'; block-all-mixed-content; upgrade-insecure-requests; sandbox allow-same-origin allow-scripts; require-sri-for script style",
  "applications": {
    "gecko": {
      "id": "about-black@apps.jeurissen.co"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "about-black@apps.jeurissen.co"
    }
  },
  "background": {
    "page": "/views/background.html",
    "persistent": false
  },
  "icons": {
    "16": "/images/icon.svg",
    "32": "/images/icon.svg",
    "48": "/images/icon.svg",
    "96": "/images/icon.svg",
    "128": "/images/icon.svg",
    "256": "/images/icon.svg"
  },
  "content_scripts": [
    {
      "run_at": "document_start",
      "match_about_blank": true,
      "matches": [
        "about:blank"
      ],
      "css": [
        "/styles/content-script.css"
      ]
    }
  ]
}