OpenBox desktop environment, GTK 4.12 applications, themes create ugly shadows in menus, used CSS to remove some but not all gone

Issue

I have recently switched to the OpenBox desktop environment changing from XFCE. My GTK 4.12 applications are running well, but I noted that all drop down menus have ugly shadows around them. I have created some CSS and managed to remove some of the shadows but when you have a menu containing multiple levels of submenus then only the first submenu (from the main menu bar) has the shadows removed and then all subsequent menus have a shadow at the bottom of the menu. It looks ugly and I'd like to remove it but cannot work out why the CSS that I have created does not work. The CSS is as follows:

popover contents 
{ 
   border: 1px solid black;
   border-radius: 0;
   border-width: 1px;
   box-shadow: none;
};

I have looked at the CSS information for GTK 3.x and 4.x and cannot find a way forward. I have used GTK Inspector and noticed that when I access a submenu that "tooltip" pops up in the CSS nodes section. I could not work out a way of keeping it on the screen so that I could then look at the CSS nodes and maybe work something out. Searches for popover and tooltip did not find any results.

Solution

1. Install picom

sudo apt install picom

2. Start picom on boot. This can be done by many ways depending on the desktop environment. In Openbox add the following line in ~/.config/openbox/autostart. In other X desktops use the file ~/.xprofile instead.

picom &

3. Configure picom to remove shadows. Even after installing picom some weird shadows could still be visible in ~/.config/picom.conf add the following lines (or modify them if already existing):

shadow = false;

wintypes:
{
  dropdown_menu = { shadow = false; }
  popup_menu = { shadow = false; }
  utility = { shadow = false; }
};

Answered By - evening_g