Examine source code of Winter - Here

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Winter - Here",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/0.jpg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "left center"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(196, 173, 191)",
      "toolbar_text": "rgb(43, 45, 58)",
      "frame": "rgb(143, 128, 163)",
      "tab_background_text": "rgb(0, 0, 0)",
      "toolbar_field": "rgb(90, 87, 108)",
      "toolbar_field_text": "rgb(254, 220, 219)",
      "tab_line": "rgb(90, 87, 108)",
      "popup": "rgb(255, 255, 255)",
      "popup_text": "rgb(43, 45, 58)",
      "sidebar_border": "rgb(143, 128, 163)",
      "tab_loading": "rgb(90, 87, 108)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{6319e02c-b83e-4ec1-95a2-4a3d984ca8b1}"
    }
  }
}