Examine source code of Grey boxes

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Grey boxes",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-005-f5f3cf677b1f132c75ddc7bd319dd1fc.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(225, 234, 239)",
      "toolbar_text": "rgb(79, 79, 72)",
      "frame": "rgb(145, 152, 159)",
      "tab_background_text": "rgb(255, 255, 255)",
      "toolbar_field": "rgb(255, 255, 255)",
      "toolbar_field_text": "rgb(70, 93, 76)",
      "tab_line": "rgb(244, 167, 185)",
      "popup": "rgb(255, 255, 255)",
      "popup_text": "rgb(112, 124, 116)",
      "tab_loading": "rgb(244, 167, 185)"
    }
  }
}