It's a new installation of Ubuntu 18.04. The Geany editor was installed by apt, but I'm getting a lot of console messages like below during running it:
(geany:4024): Gtk-WARNING **: 17:48:22.265: Error loading theme icon 'document-new' for stock: Icon 'document-new' not present in theme elementary-xfce-darker
(geany:4024): Gtk-WARNING **: 17:48:22.422: Error loading theme icon 'document-open' for stock: Icon 'document-open' not present in theme elementary-xfce-darker
(geany:4024): Gtk-WARNING **: 17:48:22.424: Error loading theme icon 'document-save' for stock: Icon 'document-save' not present in theme elementary-xfce-darker
(geany:4024): Gtk-WARNING **: 17:48:22.424: Error loading theme icon 'document-revert' for stock:
(geany:4024): Gtk-WARNING **: 17:48:22.425: Error loading theme icon 'window-close' for stock: Icon 'window-close' not present in theme elementary-xfce-darker
(geany:4024): Gtk-WARNING **: 17:48:22.425: Error loading theme icon 'go-previous' for stock:
(geany:4024): Gtk-WARNING **: 17:48:22.425: Error loading theme icon 'go-next' for stock:
(geany:4024): Gtk-WARNING **: 17:48:22.427: Error loading theme icon 'system-run' for stock: Icon 'system-run' not present in theme elementary-xfce-darker
(geany:4024): Gtk-WARNING **: 17:48:22.428: Error loading theme icon 'edit-clear' for stock:
(geany:4024): Gtk-WARNING **: 17:48:22.429: Error loading theme icon 'edit-clear' for stock:
(geany:4024): Gtk-WARNING **: 17:48:22.429: Error loading theme icon 'application-exit' for stock: Icon 'application-exit' not present in theme elementary-xfce-darker
(geany:4024): Gtk-WARNING **: 17:48:22.435: Error loading theme icon 'window-close' for stock: Icon 'window-close' not present in theme elementary-xfce-darker
(geany:4024): Gtk-WARNING **: 17:48:25.021: Error loading theme icon 'window-close' for stock: Icon 'window-close' not present in theme elementary-xfce-darker
How to fix that?