Examine source code of Umber

{
  "manifest_version": 2,
  "name": "Umber",
  "version": "1.0.1",
  "description": "Umber palette family — Umber (Firefox theme).",
  "author": "viscous-values",
  "homepage_url": "https://github.com/viscous-values/umber",
  "browser_specific_settings": {
    "gecko": {
      "id": "umber@viscous-values"
    }
  },
  "icons": {
    "48": "icons/icon-48.png",
    "96": "icons/icon-96.png",
    "128": "icons/icon-128.png"
  },
  "theme": {
    "colors": {
      "frame": "#26221E",
      "frame_inactive": "#2D2823",
      "toolbar": "#2D2823",
      "toolbar_top_separator": "#363029",
      "toolbar_bottom_separator": "#363029",
      "toolbar_vertical_separator": "#363029",
      "toolbar_field": "#363029",
      "toolbar_field_text": "#F0E5D0",
      "toolbar_field_border": "#48413A",
      "toolbar_field_focus": "#48413A",
      "toolbar_field_text_focus": "#E1CDA5",
      "toolbar_field_border_focus": "#D4BC91",
      "toolbar_field_highlight": "#D4BC91",
      "toolbar_field_highlight_text": "#26221E",
      "tab_text": "#E1CDA5",
      "tab_loading": "#D4BC91",
      "tab_line": "#D4BC91",
      "tab_selected": "#363029",
      "tab_background_text": "#A89986",
      "tab_background_separator": "#363029",
      "bookmark_text": "#E1CDA5",
      "icons": "#A89986",
      "icons_attention": "#E5C07B",
      "popup": "#2D2823",
      "popup_text": "#F0E5D0",
      "popup_border": "#48413A",
      "popup_highlight": "#363029",
      "popup_highlight_text": "#E1CDA5",
      "sidebar": "#2D2823",
      "sidebar_text": "#F0E5D0",
      "sidebar_border": "#363029",
      "sidebar_highlight": "#D4BC91",
      "sidebar_highlight_text": "#26221E",
      "button_background_hover": "#363029",
      "button_background_active": "#48413A",
      "ntp_background": "#26221E",
      "ntp_text": "#E1CDA5",
      "ntp_card_background": "#2D2823",
      "address_bar_box_text": "#F0E5D0",
      "address_bar_box_focus": "#48413A",
      "tab_attention": "#E5C07B"
    },
    "properties": {
      "color_scheme": "dark",
      "content_color_scheme": "system"
    }
  }
}