Using QListView or QTableView you can see that style is not what you can expect on Mac platform. As solution you can use next qstylesheet code to apply
to your widgets:
horizontalHeader()->setStyleSheet("\
QHeaderView {\
background-color: qlineargradient(x1:0, y1:0, x2:0, y2:1,\
stop:0 #ffffff, stop:0.5 #e0e0e0, stop:1 #ffffff);\
}\
QHeaderView::section {\
background-color: qlineargradient(x1:0, y1:0, x2:0, y2:1,\
stop:0 #ffffff, stop:0.5 #e0e0e0, stop:1 #ffffff);\
border: 1px solid #a0a0a0;\
border-top: 0px;\
border-left: 0px;\
padding-left: 4px; \
padding-right: 4px; \
}\
QHeaderView::section:checked {\
background-color: qlineargradient(x1:0, y1:0, x2:0, y2:1,\
stop:0 #bfd5ea, stop:0.5 #5497d9, stop:1 #bfd5ea);\
}\
QHeaderView::section:pressed {\
background-color: qlineargradient(x1:0, y1:0, x2:0, y2:1,\
stop:0 #b0c6db, stop:0.5 #4588ca, stop:1 #b0c6db);\
}");