def get_strokes(self):
        """Return a css snippet containing all stroke style options"""

        def stroke_dict_to_css(stroke, i=None):
            """Return a css style for the given option"""
            css = [
                '%s.series%s {\n' %
                (self.id, '.serie-%d' % i if i is not None else '')
            ]
            for key in ('width', 'linejoin', 'linecap', 'dasharray',
                        'dashoffset'):
                if stroke.get(key):
                    css.append('  stroke-%s: %s;\n' % (key, stroke[key]))
            css.append('}')
            return '\n'.join(css)

        css = []
        if self.graph.stroke_style is not None:
            css.append(stroke_dict_to_css(self.graph.stroke_style))
        for serie in self.graph.series:
            if serie.stroke_style is not None:
                css.append(stroke_dict_to_css(serie.stroke_style, serie.index))

        for secondary_serie in self.graph.secondary_series:
            if secondary_serie.stroke_style is not None:
                css.append(
                    stroke_dict_to_css(
                        secondary_serie.stroke_style, secondary_serie.index
                    )
                )
        return '\n'.join(css)
Return a css snippet containing all stroke style options