Examine source code of plum black background

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "plum with black background",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-026-829b05416f823e170310e7c826ad1bec.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(125, 0, 60)",
      "toolbar_text": "rgb(240, 240, 240)",
      "frame": "rgb(0, 0, 0)",
      "tab_background_text": "rgb(240, 240, 240)",
      "toolbar_field": "rgb(0, 0, 0)",
      "toolbar_field_text": "rgb(240, 240, 240)",
      "tab_line": "rgb(35, 205, 179)",
      "popup": "rgb(0, 0, 0)",
      "popup_text": "rgb(240, 240, 240)",
      "button_background_hover": "rgb(125, 0, 60)",
      "icons": "rgb(0, 0, 0)",
      "ntp_background": "rgb(0, 0, 0)",
      "ntp_text": "rgb(35, 205, 179)",
      "popup_border": "rgb(35, 205, 179)",
      "popup_highlight_text": "rgb(0, 0, 0)",
      "popup_highlight": "rgb(35, 205, 179)",
      "sidebar_border": "rgb(35, 205, 179)",
      "sidebar_highlight_text": "rgb(0, 0, 0)",
      "sidebar_highlight": "rgb(35, 205, 179)",
      "sidebar_text": "rgb(240, 240, 240)",
      "sidebar": "rgb(0, 0, 0)",
      "tab_background_separator": "rgb(35, 205, 179)",
      "toolbar_field_border_focus": "rgb(35, 205, 179)",
      "toolbar_field_focus": "rgb(0, 0, 0)",
      "toolbar_field_highlight_text": "rgb(0, 0, 0)",
      "toolbar_field_highlight": "rgb(35, 205, 179)",
      "toolbar_field_separator": "rgb(0, 0, 0)",
      "toolbar_field_text_focus": "rgb(240, 240, 240)",
      "toolbar_vertical_separator": "rgb(35, 205, 179)",
      "tab_loading": "rgb(35, 205, 179)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{c4724670-c37c-4824-aa68-5f814f83c70e}"
    }
  }
}