'Given an XBlock\'s usage locator as a string, return one of its action
buttons.
action is \'edit\', \'duplicate\', or \'delete\''

def _action_btn_for_xblock_id(self, xblock_id, action):

    return self._div_for_xblock_id(xblock_id)[0].find_element_by_css_selector('.header-actions    .{action}-button.action-button'.format(action=action))
