Examine source code of Docjava dark mode!

{
  "name": "Docjava dark mode!",
  "description": "Turns the webpage into a dark mode version..\nProgram by Guacamoleboy",
  "version": "1.1",
  "browser_specific_settings": {
    "gecko": {
      "id": "cph-jl325@cphbusiness.dk"
    }
  },
  "manifest_version": 3,
  "icons": {
    "16": "images/16.png",
    "48": "images/48.png",
    "128": "images/128.png"
  },
  "content_scripts": [
    {
      "matches": [
        "http://www.docjava.dk/*"
      ],
      "css": [
        "scripts/guac.css"
      ]
    },
    {
      "matches": [
        "https://www3.ntu.edu.sg/*"
      ],
      "css": [
        "scripts/ntu.css"
      ],
      "run_at": "document_end",
      "world": "MAIN"
    }
  ]
}