Lucid menu appears changed by emacs-29

[Colin Baxter]

I compile emacs using lucid as the x-toolkit. I also use menu-bar-open
<f10>, with my theme file containing the line

--8<---------------cut here---------------start------------->8---

'(menu ((((type x-toolkit)) (:background "grey20" :foreground "white" :box 
(:line-width 2 :color "white" :style released-button)))))

--8<---------------cut here---------------end--------------->8---

This works well in emacs-28.1 with the menu lines appearing white on a
grey20 background and remaining so whenever a selected box is raised.

Up until recently this also worked well in emacs-29.0.50. Now however in
emacs-28.0.50, a selected menu line appears black on the grey20
background, which makes it difficult to read.

Retaining the grey20 background, how can I ensure that a selected menu
line does not change to black but stays white in emacs-29.0.1? I prefer
to use a lisp solution rather than modify ~/.Xdefaults.

Thank you.

Colin Baxter.