Background of xfce4-topmenu-plugin?

Question

linux

Delivered xfce4-topmenu-plugin by manual compilation

autoreconf -i
./configure --prefix=/usr --with-gtk=3 --with-wnck=wnck1 --disable-static --disable-mate-applet --enable-xfce-applet --libexecdir=/usr/lib/topmenu
make -j3
make install

And I registered its initialization in ~/.gtkrc-2.0 and ~/.gtkrc-3.0
When it is added to my _transparent_ panel, it has a background color that matches the background color of the window title, and when a window is selected, it gets the color of the menubar itself, which is listed in the theme, but it doesn't look very good on my transparent panel and I would like to set a transparent background for it.
Tried to change the default content in gtkrc (in the theme) to the following

bg[NORMAL] = shade(0.0, @fg_color)
    engine "murrine"
    {
        #options
        rgba                = TRUE
    }

But, in the end, I get a black background when the window is selected and the same gray when the window is not selected.
Orchis theme
How to solve this problem?