Examine source code of WdBlock

{
  "manifest_version": 2,
  "name": "WdBlock",
  "version": "1.0",
  "description": "Blocks annoying donation ads on Wikipedia.",
  "icons": {
    "48": "wdblock_icon.png"
  },
  "content_scripts": [
    {
      "matches": [
        "*://*.wikipedia.org/*"
      ],
      "css": [
        "wdblock.css"
      ]
    }
  ]
}