Examine source code of InStream dark mode toggle

{
  "manifest_version": 2,
  "name": "InStream dark mode toggle",
  "short_name": "instream-dark-mode-toggle",
  "version": "1.0.0",
  "author": "instream-de",
  "homepage_url": "https://github.com/instream-de/instream-dark-mode-toggle",
  "description": "Toggle websites between dark-mode and light mode via standard CSS",
  "icons": {
    "48": "icons/system_48x48.png",
    "96": "icons/system_96x96.png"
  },
  "browser_action": {
    "browser_style": true,
    "default_icon": {
      "48": "icons/system_48x48.png",
      "96": "icons/system_96x96.png"
    },
    "default_title": "Toggle websites between dark-mode/light-mode/system-inherit"
  },
  "commands": {
    "_execute_browser_action": {
      "suggested_key": {
        "default": "Ctrl+Shift+L"
      }
    }
  },
  "permissions": [
    "storage",
    "browserSettings"
  ],
  "background": {
    "scripts": [
      "background.js"
    ]
  },
  "options_ui": {
    "page": "/options.html",
    "browser_style": true
  },
  "applications": {
    "gecko": {
      "id": "instream-dark-mode-toggle@instream.de"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "instream-dark-mode-toggle@instream.de"
    }
  }
}