Examine source code of Better dark mode

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "better dark mode",
  "theme": {
    "images": {
      "additional_backgrounds": [
        "images/bg-000-5672c42860d5b06e1058dc477397f3ef.svg"
      ]
    },
    "properties": {
      "additional_backgrounds_alignment": [
        "top"
      ],
      "additional_backgrounds_tiling": [
        "repeat"
      ]
    },
    "colors": {
      "toolbar": "rgb(23, 23, 23)",
      "toolbar_text": "rgb(185, 185, 185)",
      "frame": "rgb(13, 13, 13)",
      "tab_background_text": "rgb(255, 255, 255)",
      "toolbar_field": "rgb(53, 53, 53)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgb(37, 37, 37)",
      "popup": "rgb(36, 36, 36)",
      "popup_text": "rgb(255, 255, 255)",
      "button_background_active": "rgb(38, 38, 38)",
      "button_background_hover": "rgb(39, 39, 40)",
      "icons": "rgb(255, 255, 255)",
      "ntp_text": "rgb(255, 255, 255)",
      "popup_border": "rgb(47, 47, 47)",
      "sidebar_border": "rgb(33, 33, 33)",
      "sidebar_highlight_text": "rgb(255, 255, 255)",
      "sidebar_text": "rgb(255, 255, 255)",
      "sidebar": "rgb(21, 21, 21)",
      "tab_selected": "rgb(49, 49, 49)",
      "tab_text": "rgb(255, 255, 255)",
      "toolbar_bottom_separator": "rgb(38, 38, 38)",
      "toolbar_field_highlight": "rgba(147, 147, 147, 0.34)",
      "tab_loading": "rgb(37, 37, 37)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{838d3375-2656-4efb-9059-9a042fc0489b}"
    }
  }
}