Omarchy's White and Vantablack themes name the icon theme Yaru-grey, which does not exist, so that GTK falls back to Adwaita's monochrome icons. siv looked only in the named theme, its parents, and hicolor, so the reader's buttons kept their icons' room and drew none. siv a735cfc4 falls back to Adwaita and gnome before hicolor, as GTK does.