Examine source code of 3D Rectangles

{
  "name": "Rectangle",
  "manifest_version": 2,
  "version": "2.0",
  "theme": {
    "images": {
      "theme_frame": "squares-2.png"
    },
    "colors": {
      "frame": "rgba(229, 230, 232, 1)",
      "tab_background_text": "rgba(255, 255, 255, 1)",
      "toolbar": "rgba(102, 102, 102, 0.88)",
      "bookmark_text": "rgba(255, 255, 255, 1)",
      "toolbar_field": "rgba(122, 39, 39, 1)",
      "toolbar_field_text": "rgba(255, 255, 255, 1)",
      "tab_line": "rgba(255, 255, 255, 1)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{dedb3782-600f-463f-bcb9-a12e54a805a3}"
    }
  }
}