Examine source code of Safari Adaptive Dark

{
  "manifest_version": 2,
  "name": "Safari Adapt Dark",
  "version": "2019.1102",
  "description": "Even better with Safari-Theme-for-Firefox: https://git.io/JeBLr",
  "icons": {
    "48": "dark48.png",
    "96": "dark96.png",
    "256": "dark256.png"
  },
  "theme": {
    "colors": {
      "toolbar": "#484848",
      "toolbar_text": "#ffffff",
      "frame": "#2b2b2b",
      "tab_background_text": "#c7c7c7",
      "toolbar_field": "#6f6f6f",
      "toolbar_field_text": "#ffffff",
      "tab_line": "#4f4f4f",
      "popup": "#262626",
      "popup_text": "#d7d7d7",
      "tab_loading": "#555555",
      "tab_background_separator": "#7f7f7f",
      "toolbar_top_separator": "#5f5f5f",
      "toolbar_bottom_separator": "#000000",
      "toolbar_vertical_separator": "#000000ff",
      "tab_selected": "#3e3e3e",
      "sidebar": "#262626",
      "ntp_background": "#262626",
      "sidebar_text": "#dedede",
      "ntp_text": "#dedede",
      "popup_highlight": "#3992f1",
      "popup_highlight_text": "#ffffff",
      "button_background_active": "#6f6f6f",
      "button_background_hover": "#6f6f6f",
      "frame_inactive": "#333333"
    }
  }
}