Examine source code of Letter Shock

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "BrownPaper",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-000-5672c42860d5b06e1058dc477397f3ef.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(80, 70, 64)",
      "toolbar_text": "rgb(255, 255, 255)",
      "frame": "rgb(124, 116, 112)",
      "tab_background_text": "rgb(228, 228, 228)",
      "toolbar_field": "rgb(225, 219, 219)",
      "toolbar_field_text": "rgb(100, 76, 75)",
      "tab_line": "rgb(190, 101, 96)",
      "popup": "rgb(225, 219, 219)",
      "popup_text": "rgb(45, 39, 35)",
      "tab_loading": "rgb(190, 101, 96)"
    }
  }
}