This script automatically extends the changes in theme when the dark mode is enabled. It checks the status of that switch every 15 minutes.
It is possible to customize a light theme and a dark theme indipendently for the user interface in GNOME. It is also possible to set other light and dark themes for specific applications.
Download the archive and unpack it. cd into the uncompressed folder and give the following command from the terminal:
$ chmod +x NightModeExtender.sh ; mv NightModeExtender.sh ~/.NightModeExtender.sh ; mv NightModeExtender.desktop ~/.config/autostart/
Then reboot.
Open the script .NightModeExtender.sh and set the name of your favourite themes in the first lines.
Some apps like Libreoffice overwrites the changes set by this script if they're open when the dark mode is enabled.
JustPerfection is the original author of the script that I slightly edited. I really really really want to thank him for his help and availability. THANK YOU, JUSTPY!