Examine source code of Ječná Tools

{
  "manifest_version": 2,
  "name": "JecnaTools",
  "version": "1.0",
  "description": "Adds avarage of your grades to the grades table.",
  "icons": {
    "48": "icons/icon_48.png",
    "96": "icons/icon_96.png"
  },
  "content_scripts": [
    {
      "matches": [
        "https://www.spsejecna.cz/score/student*"
      ],
      "js": [
        "gradeAverages/script.js"
      ],
      "css": [
        "gradeAverages/styles.css"
      ],
      "run_at": "document_idle"
    }
  ]
}