Examine source code of CRZP-download-button

{
  "description": "Adds a download link where its missing on http://opac.crzp.sk website.",
  "manifest_version": 2,
  "name": "CRZP-download",
  "version": "1.0",
  "homepage_url": "https://github.com/ppiliar/crzp-dl-extension",
  "icons": {
    "48": "icons/icon-48.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://opac.crzp.sk/*"
      ],
      "js": [
        "download.js"
      ]
    }
  ]
}