Supporters of Javier Milei celebrated in the streets of Buenos Aires on Sunday after he won Argentina's presidential election runoff.Outside his party's headquarters, a hotel in downtown Buenos Aires, a full-on party kicked off with supporters singing and waving flags.With 99.4 of votes tallied in the presidential runoff, Milei had 55.7 and Economy Minister Sergio Massa 44.3, according to Argentina's electoral authority.