I have installed communitheme in gnome-shell. It gives smoother and faster experience. However, I am facing the following issue with System Monitor window. The window is completely transparent.
is there any way to solve this in this theme?
This is already fixed and should land in the stable channel soon: https://github.com/ubuntu/gtk-communitheme/issues/325
Thanks for reporting, best regards
This happens with the calculator and other default apps as well. Default apps are installed in 18.04 through "snap", a new cross-OS package manager. Snap will be much better than APT one day, but right now it's in the beginning stages and experiencing growing pains.
One of these growing pains is that it "themes" each application differently than it has in the past, and some of the new "theming" hasn't had the kinks worked out yet.
Luckily, the workaround is very very easy. Just uninstall with snap and reinstall with APT.
sudo snap remove gnome-system-monitor sudo apt install gnome-system-monitor
You might want to do this with gnome-calculator, too. I'm still looking for other applications that have this issue.