I am still researching this topic, but one of the solution is to try to force dark theme:
gsettings set org.gnome.desktop.interface color-scheme 'prefer-dark'
which didn’t do anything.
I am not big on light theme, and prefer dark, so if someone has an idea of what to do or where to look, please let me know. I am totally fine with default GNOME dark theme
OK, little progress, it seems that user theme for GNOME shell is not installed or not running.
I have not been able to find user theme for GNOME shell in AUR, and I have not been able to install it directly from browser. I have never been able to enable extension by downloading it from GNOME extensions.