Transparency missing everywhere

[thistlillo]

In my Regolith 2.0 installation on a Ubuntu 20.04 (installed via package manager) all the transparency effects (I have with the normal GNOME environment) are missing. I do not care about transparency introduced for aesthetics reasons: in some cases the full opacity of graphical elements makes the system less usable.

The attached screenshot shows what I see on screen when I move two email messages within Thunderbird. As you can see, what would normal be transparent (the space between the two selected messages) is full gray and prevents me from seeing which folder I am moving the two messages into.

The problem is there also when you select and move multiple consecutive email messages: they are not transparent, so you do not see what your mouse is hovering.

I made some searches, but I could not find anything about this (preventive sorry if I used the wrong keywords). However, I think that the default behaviour should use transparency.