Did you miss the general idea of this topic and all of the previous posts including the one with pictures outlining how your ‘solution’ does not suffice ?
I may have partly missed it (even If I don’t get the use case : transparency makes it impossible to use.)
Obviously ~/.config/gtk-3.0/gtk.css #whiskermenu-window settings do not allow opacity or background=none.
Stuff I learned in the process is to relaunch with this :
killall -HUP xfce4-panel
or
xfce4-panel -r
Ah to be fair it looks like the second pic got reduced to the hyperlink only. 
My wording may have been bad,sorry about that ,when I said side bar I meant the menu your arrow pointed to,
–see second picture
what I want is the white bit(the one with the terminal,firefox and stuff) to be also transparent
EDIT: Here’s a solution that’s suitable for all kinds of backgrounds/wallpapers, not just dark ones.
The steps are as follows:
Composite (in xfwm settings) must be activated and opacity must be lowered to at least 99% within whisker menu > properties for this to work!
Create and edit this .css file from terminal:
nano ~/.config/gtk-3.0/gtk.css
Paste this into it:
#whiskermenu-window {
background-color: rgba(0,0,0,0.7);
color: #ccc;
}
#whiskermenu-window button {
background-color: transparent;
color: #ccc;
}
#whiskermenu-window button:hover {
background-color: transparent;
color: #fff;
}
#whiskermenu-window button:checked {
background-color: transparent;
color: #fff;
}
#whiskermenu-window treeview {
background-color: transparent;
color: #ccc;
}
#whiskermenu-window treeview:hover {
background-color: transparent;
color: #fff;
}
Save the file by pressing:
Strg+O
(Confirm with ENTER), then exit nano:
Strg+X
Finally restart whisker menu:
xfce4-panel -r
Enjoy!
Wallpaper by @Lunix
(The resulting look from the code posted above differs slightly from the whisker menu in the screenshot in order to make it work with brighter backgrounds as well)
3 Likes
You did what I want but it didn’t work for me,when I restart the panel this message gets printed to the terminal:
Gtk-Message: 15:39:10.014: Failed to load module “colorreload-gtk-module”
and the whisker menu stays at the same style as it was before
EDIT:Thank you and everyone who replied.
1 Like
Do you have any custom themes installed/applied?
yes,I have the “zorin-grey-dark” theme
I will try to disable it and see
EDIT:switching to “mutcha sea” makes the app tree semi transparent,not fully
Would you mind switching to any of the matcha dark themes and try again?
they all make the app tree semi transparent(not fully)
Is there any error message now after restarting whisker?
Yes,this
Gtk-Message: 16:33:39.633: Failed to load module "colorreload-gtk-module"
Beauty doesn’t have to be useful. 
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When playing around with the .css file I mostly got errors when there were any syntax errors.
Could you delete the .css file and create a new one, then paste the above content as is? You can use a file manager for that instead of nano.
ok will do it and update
I assume that you have both composite enabled and lowered opacity within whisker settings…
1 Like
After tinkering around doing what you said + removing some things unnecessary things I put off of the gtk-3.0 folder
I no longer get an error when restarting the panel,but still I get semi transparent menu
EDIT: What is the output of
nano ~/.config/xfce4/panel/whiskermenu-8.rc
The file doesn’t exist so it says new file