pocillo is the default GTK theme for Ubuntu Budgie 20.04 and newer.
snap install gtk-theme-pocillo
To connect the theme to a snapped application, you can run:
sudo snap connect [other snap]:gtk-3-themes gtk-theme-pocillo:gtk-3-themes
sudo snap connect [other snap]:gtk-2-themes gtk-theme-pocillo:gtk-2-themes
Or, you can connect the pocillo snapped theme to all snapped apps that support theme plugs:
for PLUG in $(snap connections | grep gtk-common-themes:gtk-3-themes | awk '{print $2}'); do sudo snap connect ${PLUG} gtk-theme-pocillo:gtk-3-themes; done
for PLUG in $(snap connections | grep gtk-common-themes:gtk-2-themes | awk '{print $2}'); do sudo snap connect ${PLUG} gtk-theme-pocillo:gtk-2-themes; done
An official snap built with ❤︎ by the Ubuntu Budgie team using configuration at https://github.com/ubuntubudgie/gtk-theme-pocillo-snap and the Pocillo theme from source https://github.com/ubuntubudgie/pocillo-gtk-theme.