Examine source code of Webtoons dark mode

{
  "manifest_version": 2,
  "name": "Webtoons dark mode",
  "version": "1.0",
  "description": "Changes background color from white to black",
  "icons": {
    "48": "icons/webtoondarkmode-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.webtoons.com/*viewer*"
      ],
      "js": [
        "webtoondarkmode.js"
      ]
    }
  ]
}