This is the patched version of libAdwaita in Linux Mint 22.
It is based on libAdwaita 1.5 and adds theme support.
The library uses the current GTK3 theme. If it provides a libadwaita-1.5 directory, it uses the theme's stylesheets. Otherwise it fallsback to the library's own stylesheet, which looks exactly the same as upstream libadwaita.
Inside the theme's libadwaita-1.5 directory, there should be the following CSS files:
defaults-light.cssdefines the colors in Light modedefaults-dark.cssdefines the colors in dark modebase.cssdefines the widgets stylebase-hc.cssdefines the widgets style in high-contrast modeassetsprovide pictures used by the stylesheet
You can find these files in /usr/share/themes/LibAdwaita-Example/libadwaita-1.5 after installing the libadwaita-1-examples package.
To minimize potential issues it is recommended to only change the colors and the style of the window controls.
The best place to modify the window controls is at the bottom of base.css.
If your theme uses SASS you can work from the SASS files directly and get greater control.
In this case, you can find the stylesheet here in the src/stylesheet directory.
Mint-X and Mint-Y implement support for this library.
You can find their stylesheets in /usr/share/themes/Mint-X/libadwaita-1.5 and /usr/share/themes/Mint-Y/libadwaita-1.5, or on github at https://github.com/linuxmint/mint-themes/tree/master/files/usr/share/themes.