Examine source code of red grid

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "czerwona krata",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.png"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "center top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgba(7, 50, 84, 0)",
      "toolbar_text": "rgb(191, 191, 191)",
      "frame": "rgb(0, 0, 0)",
      "tab_background_text": "rgb(166, 166, 166)",
      "toolbar_field": "rgba(60, 59, 59, 0.74)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgb(191, 191, 191)",
      "popup": "rgb(0, 0, 0)",
      "popup_text": "rgb(255, 28, 0)",
      "ntp_background": "rgb(52, 52, 52)",
      "tab_loading": "rgb(191, 191, 191)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{7804a315-de47-4f01-9b92-782179a69d0f}"
    }
  }
}