Draw a frame around the figure viewer if state is True.

def show_fig_outline_in_viewer(self, state):
        """Draw a frame around the figure viewer if state is True."""
        if state is True:
            self.figviewer.figcanvas.setStyleSheet(
                    "FigureCanvas{border: 1px solid lightgrey;}")
        else:
            self.figviewer.figcanvas.setStyleSheet("FigureCanvas{}")
        self.option_changed('show_plot_outline', state)