Examine source code of Dev28

{
  "name": "Dev28",
  "manifest_version": 2,
  "version": "89.15",
  "theme": {
    "images": {},
    "colors": {
      "bookmark_text": "#fff",
      "icons": "#aaa",
      "frame": "#282828",
      "ntp_background": "#111",
      "ntp_text": "#fff",
      "popup": "#fff",
      "popup_border": "#0000",
      "popup_highlight": "#ccc",
      "popup_highlight_text": "#000",
      "popup_text": "#000",
      "sidebar": "#fff",
      "sidebar_border": "#fff",
      "sidebar_highlight": "#bbb",
      "sidebar_highlight_text": "#000",
      "sidebar_text": "#000",
      "tab_background_text": "#aaa",
      "tab_line": "#383838",
      "tab_selected": "#383838",
      "tab_text": "#fff",
      "toolbar": "#282828",
      "toolbar_field": "#222",
      "toolbar_field_focus": "#222",
      "toolbar_field_highlight": "#333",
      "toolbar_field_highlight_text": "#fff",
      "toolbar_field_text": "#aaa",
      "toolbar_field_text_focus": "#aaa",
      "toolbar_text": "#aaa",
      "toolbar_field_border": "rgba(0, 0, 0, 0)",
      "toolbar_field_border_focus": "rgba(0, 0, 0, 0)",
      "toolbar_bottom_separator": "rgba(0, 0, 0, 0)",
      "toolbar_top_separator": "rgba(0, 0, 0, 0)"
    }
  },
  "browser_specific_settings": {
    "gecko": {
      "id": "{af4bfa90-91ce-4bcd-b8dd-6b926723aca2}"
    }
  }
}