I tried visiting the enclosed theme from the `custom-create-theme'
buffer, and got:
--8<---------------cut here---------------start------------->8---
Debugger entered--Lisp error: (invalid-function (menu-bar-lines . 1))
  ((menu-bar-lines . 1) (tool-bar-lines . 0))
  eval(((menu-bar-lines . 1) (tool-bar-lines . 0)))
  custom-theme-recalc-variable(default-frame-alist)
  disable-theme(system-type-darwin)
  load-theme(system-type-darwin)
  custom-theme-merge-theme(system-type-darwin)
  call-interactively(custom-theme-merge-theme)
  custom-theme-visit-theme()
  call-interactively(custom-theme-visit-theme)
  #[(widget &optional event) "\300\301!\207" [call-interactively custom-theme-visit-theme] 2]((push-button :tag "Visit Theme" :help-echo "Insert the settings of a pre-defined theme." :action #[(widget &optional event) "\300\301!\207" [call-interactively custom-theme-visit-theme] 2] :button-overlay #<overlay from 318 to 329 in *New Custom Theme*> :from #<marker (moves after insertion) at 318 in *New Custom Theme*> :to #<marker at 329 in *New Custom Theme*>) nil)
  widget-apply((push-button :tag "Visit Theme" :help-echo "Insert the settings of a pre-defined theme." :action #[(widget &optional event) "\300\301!\207" [call-interactively custom-theme-visit-theme] 2] :button-overlay #<overlay from 318 to 329 in *New Custom Theme*> :from #<marker (moves after insertion) at 318 in *New Custom Theme*> :to #<marker at 329 in *New Custom Theme*>) :action nil)
  widget-apply-action((push-button :tag "Visit Theme" :help-echo "Insert the settings of a pre-defined theme." :action #[(widget &optional event) "\300\301!\207" [call-interactively custom-theme-visit-theme] 2] :button-overlay #<overlay from 318 to 329 in *New Custom Theme*> :from #<marker (moves after insertion) at 318 in *New Custom Theme*> :to #<marker at 329 in *New Custom Theme*>) nil)
  widget-button-press(318)
  call-interactively(widget-button-press nil nil)
--8<---------------cut here---------------end--------------->8---