light_button.signal_toggled().connect (sigc::mem_fun (*this, &ThemeManager::on_light_theme_button_toggled));
reset_button.signal_clicked().connect (sigc::mem_fun (*this, &ThemeManager::reset_canvas_colors));
flat_buttons.signal_toggled().connect (sigc::mem_fun (*this, &ThemeManager::on_flat_buttons_toggled));
light_button.signal_toggled().connect (sigc::mem_fun (*this, &ThemeManager::on_light_theme_button_toggled));
reset_button.signal_clicked().connect (sigc::mem_fun (*this, &ThemeManager::reset_canvas_colors));
flat_buttons.signal_toggled().connect (sigc::mem_fun (*this, &ThemeManager::on_flat_buttons_toggled));