After an application style change, the paintEvent updates the
        custom defined stylesheet.

def _refresh(self):
        """After an application style change, the paintEvent updates the
        custom defined stylesheet.
        """
        padding = self.height()
        css_base = """QLineEdit {{
                                 border: none;
                                 padding-right: {padding}px;
                                 }}
                   """
        css_oxygen = """QLineEdit {{background: transparent;
                                   border: none;
                                   padding-right: {padding}px;
                                   }}
                     """
        if self._application_style == 'oxygen':
            css_template = css_oxygen
        else:
            css_template = css_base

        css = css_template.format(padding=padding)
        self.setStyleSheet(css)
        self.update()