Examine source code of Stretching fields

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Stretching fields",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.jpg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "center bottom"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgba(234, 227, 239, 0.57)",
      "toolbar_text": "rgb(1, 9, 0)",
      "frame": "rgb(220, 203, 216)",
      "tab_background_text": "rgb(238, 235, 245)",
      "toolbar_field": "rgba(255, 255, 255, 0.21)",
      "toolbar_field_text": "rgb(4, 1, 19)",
      "tab_line": "rgb(255, 255, 255)",
      "popup": "rgb(234, 235, 246)",
      "popup_text": "rgb(153, 51, 255)",
      "tab_loading": "rgb(255, 255, 255)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{c8b1cd28-2f3e-496e-b679-8db15a57c6e2}"
    }
  }
}