'Gets all CSS content from and removes all <link rel="stylesheet"> and
<style> tags concatenating into one CSS string which is then parsed with
cssutils and the resulting CSSStyleSheet object set to
`self.stylesheet`.'

def _get_styles(self):

    self._get_external_styles()
    self._get_internal_styles()
    cssparser = cssutils.CSSParser(log=self.log)
    self.stylesheet = cssparser.parseString(self.style_string)
