To avoid ambiguity, the declaration for gtk-theme-yaru-mate should match that of gtk-theme-traditionalhumanized:
slots:
content:
allow-auto-connection:
-
plug-attributes:
content: $SLOT(content)
slot-attributes:
content: gtk-3-themes
slots-per-plug: *
-
plug-attributes:
content: $SLOT(content)
slot-attributes:
content: gtk-2-themes
slots-per-plug: *
And for icon-theme-yaru-mate it’d be:
slots:
content:
allow-auto-connection:
-
plug-attributes:
content: $SLOT(content)
slot-attributes:
content: icon-themes
slots-per-plug: *