human
Complete this python program:
def click_css(page, css, source_index=0, require_notification=True):
assistant
#Here is the Python program you requested.

    """Click the button/link with the given css and index on the specified page (subclass of PageObject).
    Will only consider elements that are displayed and have a height and width greater than zero.
    If require_notification is False (default value is True), the method will return immediately.
    Otherwise, it will wait for the "mini-notification" to appear and disappear.
    """
    def _is_visible(element):
        'Is    the    given    element    visible?'
        return (element.is_displayed() and all(((size > 0) for size in element.size.itervalues())))
    disable_animations(page)
    page.q(css=css).filter(_is_visible).nth(source_index).click()
    if require_notification:
        sync_on_notification(page)
    page.wait_for_ajax()