Examine source code of Garden Slug

{
  "theme": {
    "images": {
      "theme_frame": "1Slug.jpg"
    },
    "colors": {
      "frame": "#c9c9c9",
      "tab_background_text": "#faf5f5"
    }
  },
  "version": "2.0",
  "name": "Garden Slug",
  "manifest_version": 2,
  "description": "Brown garden slug photographed in my garden. More of the slug is visible if your browser has an extra toolbar added."
}