Update the background stylesheet to make it lighter.

def _update_stylesheet(self, widget):
        """Update the background stylesheet to make it lighter."""
        if is_dark_interface():
            css = qdarkstyle.load_stylesheet_from_environment()
            widget.setStyleSheet(css)
            palette = widget.palette()
            background = palette.color(palette.Window).lighter(150).name()
            border = palette.color(palette.Window).lighter(200).name()
            name = widget.__class__.__name__
            widget.setObjectName(name)
            extra_css = '''
                {0}#{0} {{
                    background-color:{1};
                    border: 1px solid {2};
                }}'''.format(name, background, border)
            widget.setStyleSheet(css + extra_css)