These are a few themes I found for "Ubuntu 18.04 LTS - Xubuntu 18.04 LTS" they also worked on Mint 19.3 but Mint has tons of themes by default.


First open your favorite terminal. I use "Terminator Terminal" it can be found in the Software Center.
Then run these commands: (hit enter after each one)
Copy and paste into the terminal window: sudo apt-get update
Copy and paste into the terminal window: sudo apt-get upgrade

Copy and paste into the terminal window: sudo add-apt-repository ppa:noobslab/themes
Copy and paste into the terminal window: sudo apt-get update

Copy and paste into the terminal window: sudo add-apt-repository ppa:noobslab/icons
Copy and paste into the terminal window: sudo apt-get update

Copy and paste into the terminal window: sudo apt-get install ultimate-maia-theme
Copy and paste into the terminal window: sudo apt-get update
Copy and paste into the terminal window: sudo apt-get install ultimate-maia-icons
Copy and paste into the terminal window: sudo apt-get update

Copy and paste into the terminal window: sudo apt-get install ultimate-dark-theme
Copy and paste into the terminal window: sudo apt-get update

Copy and paste into the terminal window: sudo apt-get install stylish-themes
Copy and paste into the terminal window: sudo apt-get update

Copy and paste into the terminal window: sudo apt-get install vimix-gtk-themes (you may need to add more libs I did not need to)
Copy and paste into the terminal window: sudo apt-get update
Copy and paste into the terminal window: sudo apt-get install vimix-icon-theme
Copy and paste into the terminal window: sudo apt-get update

Copy and paste into the terminal window: sudo apt-get install macbuntu-os-ithemes-v1804
Copy and paste into the terminal window: sudo apt-get update
Copy and paste into the terminal window: sudo apt-get install macbuntu-os-icons-v1804
Copy and paste into the terminal window: sudo apt-get update

You can find these on this website: https://www.noobslab.com/2018/09/ultimate-dark-ultimate-maia-themes-and.html

Now you should be able to see all the themes on you menu under "Settings - Appearance". Some as with all things have small glitches like font coloring to light or to dark.
I'm using "Adwaita Dark" 


If you have any good websites for themes please share them.

And as always any questions just ask!
This post was edited by beastusa at April 2, 2020 7:46 AM PDT