Examine source code of Return Youtube UI

{
  "manifest_version": 3,
  "name": "Return YouTube UI",
  "version": "2.3.12",
  "author": "42null",
  "description": "An extension making YouTube look like it used to before everything became rounded and circular with customisable settings.",
  "homepage_url": "https://github.com/42null/Return-YouTube-UI",
  "browser_specific_settings": {
    "gecko": {
      "id": "{6d38b91b-577a-4e14-a402-caa8e2080ccd}"
    }
  },
  "permissions": [
    "storage",
    "scripting",
    "tabs"
  ],
  "host_permissions": [
    "*://*.youtube.com/*"
  ],
  "background": {
    "scripts": [
      "background/background.js"
    ]
  },
  "action": {
    "default_icon": "icons/ReturnYouTubeUIIconV2R2_512.png",
    "theme_icons": [
      {
        "light": "icons/ReturnYouTubeUIIconV2R2_512.png",
        "dark": "icons/ReturnYouTubeUIIconV2R2_512.png",
        "size": 32
      }
    ],
    "default_title": "Return YouTube UI",
    "default_popup": "popup/popup.html"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.youtube.com/*"
      ],
      "js": [
        "triggerSetup.js",
        "injectionInjector.js"
      ]
    }
  ],
  "web_accessible_resources": [
    {
      "resources": [
        "injection_parts/helper_functions.js",
        "global_helper_functions.js",
        "injectionInjector.js",
        "injection_parts/primary/*.css",
        "injection_parts/extras/*.css",
        "projectConfiguration.json",
        "icons/*"
      ],
      "matches": [
        "*://*.youtube.com/*"
      ]
    }
  ],
  "icons": {
    "512": "icons/ReturnYouTubeUIIconV2R2_512.png"
  }
}