How to apply bumpmaps to a Cinnamon theme?

I am running Linux Mint 19.3 with Cinnamon 4.4.8. I tried to copy the .menu-background code from the end of this thread into my theme's cinnamon.css file: https://www.linuxquestions.org/quest...or-4175568882/. However, only the colors from the code were applied and the frost effect didn't work. This is despite the fact that my system indeed has the correct .png bumpmap file. I think this is related to my text editor, VS Code, complaining that background-bumpmap and other properties are unknown CSS properties. I thought that those properties were defined in the menu.js file referred to in the original thread. However, I couldn't find it inside neither the theme directories nor the cinnamon-* directories, and instead have only found popupMenu.js, which doesn't even contain the names of the unknown properties.

Since the thread mentioned above is 4 years old, is it still possible to apply bumpmaps to various elements of Cinnamon, such as the menu or the panel? If so, can you please explain me how to do it?