$ cat ~/.config/gtk-3.0/gtk.css
/*set custom gtk3/css code below */

@import url("whisker-tweak.css");

/* Widget reloj */
#xfce-panel-toggle-button { color: black }
#xfce-panel-toggle-button:hover { color: white }

.xfce4-panel widget image { color: black; }


$ cat ~/.config/gtk-3.0/settings.ini
cat: /home/Sergio/.config/gtk-3.0/settings.ini: No such file or directory