I think Palais Garnier has significant features of Beaux-Arts style. The architecture is highly ornamented with gold, and some Baroques styles like the dome with much more geographic shapes which is significantly after the Renaissance. Palais Garnier mixes few different styles together, with symmetrical design by using the 8 columns at the front floor. However, classical Greece or Italy architecture is more austere such like the Pantheon and the Parthenon, but with huge structure. The material used is also different, metals were not been used in antique architecture styles, Palais Garnier does use them.