This third-party theme back-ports the bulk of the libadwaita stylesheet to a regular GTK theme that works with GTK3 apps.
As this theme is under active development you can’t be too picky if there are a few unpadded highlights or errant pixels; it’s not a 1:1 clone of what you seen in GNOME 42 screenshots (or any GTK4 libadwaita apps you currently use) but it’s a close enough approximation.
Also: this is purely superficial; you won’t magically find GTK4 features, widgets, or animations nestled inside your GTK3 apps.
But it look great so far:
As there’s not yet been a formal stable release you’ll need build this theme from source to try it out on your system. This is made easier thanks to a comprehensive guide up on Reddit.
Compiling a theme from source sounds scary but it’s not: it only takes a few commands and a few minutes to get things up and running.
If I can do it, chances are you can too!
First, install everything you’ll need to compile the adw-gtk theme:
sudo apt install ninja-build git meson sassc
Next, clone the theme’s branch from GitHub:
git clone https://github.com/lassekongo83/adw-gtk3.git
Then enter the cloned directory:
Tell Meson to build it:
Once built (this will take seconds, if that) proceed to install the theme.
First enter the build directory:
Finally, invoke Ninja to do the rest:
sudo ninja install
Once done you can change theme to the libadwaita GTK3 theme using an app like GNOME Tweaks. Alternatively, if you wish to stay at the command line, use
gsettings like so:
gsettings set org.gnome.desktop.interface gtk-theme adw-gtk3
A dark variant is included too, if you’re a fan of dark mode.
To “undo” this change just repeat the last step but switch from the ‘adw-gtk3’ theme to the ‘Yaru’ theme.