'write style theme'

def _write_style(self, node):

    style = SubElement(node, ('{%s}style' % CHART_DRAWING_NS))
    ln_ref = SubElement(style, ('{%s}lnRef' % DRAWING_NS), {'idx': '2'})
    scheme_clr = SubElement(ln_ref, ('{%s}schemeClr' % DRAWING_NS), {'val': 'accent1'})
    SubElement(scheme_clr, ('{%s}shade' % DRAWING_NS), {'val': '50000'})
    fill_ref = SubElement(style, ('{%s}fillRef' % DRAWING_NS), {'idx': '1'})
    SubElement(fill_ref, ('{%s}schemeClr' % DRAWING_NS), {'val': 'accent1'})
    effect_ref = SubElement(style, ('{%s}effectRef' % DRAWING_NS), {'idx': '0'})
    SubElement(effect_ref, ('{%s}schemeClr' % DRAWING_NS), {'val': 'accent1'})
    font_ref = SubElement(style, ('{%s}fontRef' % DRAWING_NS), {'idx': 'minor'})
    SubElement(font_ref, ('{%s}schemeClr' % DRAWING_NS), {'val': 'lt1'})
