Examine source code of Doom Plates

{
  "theme": {
    "images": {
      "theme_frame": "doom-plates_header.jpg"
    },
    "colors": {
      "frame": "#333333",
      "tab_background_text": "#ffffff"
    }
  },
  "version": "2.0",
  "name": "Doom Plates",
  "manifest_version": 2,
  "description": "All these Doom style plates and doors were created in Filter Forge. Each plate is unique throughout the 3000px wide header and is only repeated in the footer, but since the header aligns to the right edge while the footer aligns to the left edge,  your browser is going to have to be at least 1500 pixels wide before you might notice any repetition."
}