make theme dark
Open tweaks app > Appearance > Legacy Applications > set Adwaita-dark
gnome desktop not load with correct password
First of all, try to re-install the gnome-session:
sudo apt-get update
sudo apt-get upgrade #see if the package is held back
sudo apt-get purge gnome-session
sudo apt-get install gnome-session
startx
If it did not help (bad news!), install another desktops like KDE-Plasma. After that, try to find out the error with running different desktops and see their responses! Or maybe you should re-install gnome more completely (maybe with sudo apt install gnome gdm3 task-gnome-desktop --reinstall and the sudo reboot).