Binary package “bluebird-gtk-theme” in ubuntu bionic
blue GTK+ theme from the Shimmer Project
Bluebird was the default theme for Xubuntu 10.10 but since 2011, Greybird
has been Xubuntu's default theme. As its name indicates, Bluebird is a
blue theme. The Shimmer Project are the designers and developers of both
Bluebird and Greybird.
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Bluebird works best in Xfce since it currently has incomplete support
for newer versions of GTK+ 3.