Which part of Renaissance art did Jacob Burckhardt focus on in History of the Renaissance in Italy?

In his work Die Geschichte der Renaissance in Italien (1867), Jacob Burckhardt focused exclusively on architecture.1

While Burckhardt considered art to be the saving grace of the Renaissance, he did not treat the subject in his most famous book, The Civilization of the Renaissance in Italy. He had originally hoped to cover art in a separate monograph, but that ambition was only partially fulfilled by his 1867 study, which limited its scope to architectural developments.1