Examine source code of Extremely Dark

{
  "manifest_version": 2,
  "version": "1.0",
  "name": "Pitch Black",
  "theme": {
    "images": {},
    "properties": {},
    "colors": {
      "toolbar": "rgb(0, 0, 0)",
      "toolbar_text": "rgb(255, 255, 255)",
      "frame": "rgb(0, 0, 0)",
      "tab_background_text": "rgb(215, 226, 239)",
      "toolbar_field": "rgb(0, 0, 0)",
      "toolbar_field_text": "rgb(255, 255, 255)",
      "tab_line": "rgb(255, 255, 255)",
      "popup": "rgb(0, 0, 0)",
      "popup_text": "rgb(255, 255, 255)",
      "button_background_active": "rgba(130, 130, 130, 0.35)",
      "button_background_hover": "rgb(30, 30, 30)",
      "ntp_background": "rgb(0, 0, 0)",
      "ntp_text": "rgb(255, 255, 255)",
      "tab_loading": "rgb(255, 255, 255)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{842c774a-e7ef-4a85-9940-811cbe9deef1}"
    }
  }
}