Examine source code of Double side

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Double side",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-041-f8d3c45dc76f1a30e90018697ef3830b.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgba(40, 203, 232, 0.77)",
      "toolbar_text": "rgb(255, 255, 255)",
      "frame": "rgb(226, 215, 223)",
      "tab_background_text": "rgb(119, 49, 101)",
      "toolbar_field": "rgba(151, 24, 207, 0.21)",
      "toolbar_field_text": "rgb(111, 27, 92)",
      "tab_line": "rgb(255, 255, 255)",
      "popup": "rgb(255, 255, 255)",
      "popup_text": "rgb(51, 202, 225)",
      "tab_loading": "rgb(255, 255, 255)"
    }
  }
}