This is my custom Mainsail theme using aspects from various existing themes including RatOS and Acryl. It attempts to incorporate the Primary and Logo colors, as set in the Interface Settings, in accordance with Material Design principles.
You'll first clone the repo and run the install script:
cd ~
git clone https://github.com/gethe/mainsail_theme.git
sudo -u pi bash ~/mainsail_theme/install.sh
This will create an editable custom.css file and symlink the base theme files
into /home/pi/printer_data/config/.theme.